Recovery Plan for the Mexican Spotted Owl (Strix occidentalis lucida )

Recovery Recovery Plan
Plan
for for the
the
Mexican Mexican Spotted Spotted Owl
Owl
(Strix Strix occidentalis occidentalis lucida lucida) lucida
Plan de Recuperacion
del Tecolate Moteado Mexicano
(Strix occidentalis lucida)
December 1995

Primary Primary Primary Authors:
Authors:
Recovery Recovery Plan
Plan
for for the
the
Mexican Mexican Mexican Spotted Spotted Owl
Owl
(Strix Strix occidentalis occidentalis lucida lucida) lucida
Plan de Recuperacion
del Tecolate Moteado Mexicano
(Strix occidentalis lucida)
Nancy M. Kaufman, Regional Director,
U.S. Department of the Interior, Fish and Wildlife Service,
Southwestern Region
William M. Block; Fernando Clemente; Jack F. Cully; James L. Dick, Jr.; Alan B. Franklin;
Joseph L. Ganey; Frank P. Howe; W.H. Moir; Steven L. Spangle; Sarah E. Rinkevich; Dean L. Urban;
Robert Vahle; James P. Ward, Jr.; and Gary C. White
Other Other Contributors:
Contributors:
Kevin J. Cook (Technical Editor): Brian Geils (Disturbance Analyses);
Kate W. Grandison (Meeting Facilitator); Tim Keitt (Landscape Analyses); Juan F. Martinez-Montoya
(Mexican Recovery Units); Art Needleman and Jill Simmons (Layout and Design);
Joyce V. Patterson (Illustrator); Tom Spalding (State of Arizona); Rich Teck (Forest Modeling);
Steven Thompson (Southwestern Tribal Liaison); Brenda E. Witsell (Administrative Assistant).
1995
Approved:__________________________________________________ Date:_____________
Regional Director, U.S. Fish and Wildlife Service

DISCLAIMER:
DISCLAIMER:
This Recovery Plan is not intended to provide details on all aspects of Mexican spotted owl management.
The Recovery Plan outlines steps necessary to bring about recovery of the species. The Recovery Plan is not
a “decision document” as defined by the National Environmental Policy Act (NEPA). It does not allocate
resources on public lands. The implementation of the recovery plan is the responsibility of Federal and State
management agencies in areas where the species occurs. Implementation is done through incorporation of
appropriate portions of the Recovery Plan in agency decision documents such as forest plans, park management
plans, and State game management plans. Such documents are then subject to the NEPA process for
public review and selection of alternatives.
LITERATURE LITERATURE CITATIONS:
CITATIONS:
This document should be referenced in literature citations as follows:
USDI Fish and Wildlife Service. 1995. Recovery plan for the Mexican spotted owl: Vol.I.
Albuquerque, New Mexico. XXXpp.
A fee for additional copies of this document will be charged depending on the number of pages
and postage. Additional copies of this document may be purchased from:
Fish and Wildlife Reference Service
5430 Grosvenor Lane, Suite 110
Bethesda, MD 20814
(303) 492-6403
1-800-582-3421

Mexican Spotted Owl Recovery Plan
MEXICAN MEXICAN SPO SPOTTED SPO TED O OOWL
O WL RECO RECOVER RECO VER VERY VER Y PL PLAN PL AN
Table Table of of Contents
Contents
List List of of Tables ables ables ................................................................................................................................ ................................................................................................................................ vii
vii
List List of of F FFigur
F igur igures igur es ............................................................................................................................... ............................................................................................................................... viii
viii
Executiv ecutiv ecutive ecutiv e S SSummar
S ummar ummary ummar ....................................................................................................................... ....................................................................................................................... ix
ix
Ackno ckno cknowledgments
ckno wledgments wledgments........................................................................................................................
wledgments ........................................................................................................................ xiii
xiii
PAR AR ART AR T I: I: PL PLAN PL AN DE DEVEL DE VEL VELOPMENT
VEL OPMENT
A. A. RECO RECOVER RECO RECO VER VERY VERY
Y PL PLANNING
PL ANNING ................................................................................................ ................................................................................................ 1
B. B. LISTING LISTING ............................................................................................................................ ............................................................................................................................ 2
The Present or Threatened Destruction, Modificiation, or Curtailment
of its Habitat or Range .....................................................................................................2
Overutilization for Commercial, Recreational, Scientific, or Educational
Purposes ..........................................................................................................................3
Disease or Predation ........................................................................................................ 3
Inadequacy of Existing Regulatory Mechanisms ...................................................................3
Other Natural or Manmade Factors Affecting Its Continued Existence ................................3
C. C. PP
PAST PP
AST AND AND CURRENT CURRENT MANA MANAGEMENT MANA GEMENT OF OF THE
THE
MEXICAN MEXICAN SPO SPOTTED SPO TED O OOWL
O OWL
WL .......................................................................................... .......................................................................................... 4
Fish and Wildlife Service ...................................................................................................... 4
Forest Service ....................................................................................................................... 4
Forest Service Southwestern Region (Region 3) ................................................................ 4
Forest Service Rocky Mountain Region (Region 2) .......................................................... 5
Forest Service Intermountain Region (Region 4) .............................................................. 5
Other Federal Agencies ........................................................................................................ 6
National Park Service ....................................................................................................... 6
Bureau of Land Management ........................................................................................... 6
Department of Defense ................................................................................................... 6
States ................................................................................................................................... 7
Arizona............................................................................................................................ 7
New Mexico .................................................................................................................... 7
Colorado ......................................................................................................................... 7
Utah ................................................................................................................................ 7
Texas ............................................................................................................................... 8
Tribes .................................................................................................................................. 8
Mescalero Apache Tribe ................................................................................................... 8
White Mountain Apache Tribe......................................................................................... 8
San Carlos Apache Tribe .................................................................................................. 9
Jicarilla Apache ................................................................................................................ 9
Navajo Nation ................................................................................................................. 9
Mexico ................................................................................................................................ 9
D. D. CONSIDERA
CONSIDERA
CONSIDERATIONS CONSIDERA
CONSIDERATIONS
TIONS IN IN PL PLAN PL AN DE DEVEL DE DEVEL
VEL VELOPMENT
VEL OPMENT ....................................................... ....................................................... 11
11
Recovery Units .................................................................................................................... 11
The Current Situation ......................................................................................................... 11
Recovery Plan Duration ....................................................................................................... 12
Conservation Plans for Other Spotted Owl Subspecies ......................................................... 13
i

Mexican Spotted Owl Recovery Plan
Ecosystem Management ..................................................................................................... 15
Economic Considerations ...................................................................................................16
Human Intervention and Natural Processes ........................................................................17
Differences Between the Draft and Final Recovery Plans .....................................................17
PAR AR ART AR T II: II: BIOL BIOLOGICAL BIOL OGICAL AND AND AND ECOL ECOLOGICAL ECOL OGICAL BA BACK BA CK CKGR CK GR GROUND GR OUND
A. A. GENERAL GENERAL BIOL BIOLOGY BIOL OGY AND AND AND ECOL ECOLOGICAL ECOL OGICAL REL RELATIONSHIPS
REL TIONSHIPS
OF OF THE THE MEXICAN MEXICAN SPO SPOTTED SPO TED O OOWL
O WL ......................................................................... ......................................................................... 19
19
Taxonomy ..........................................................................................................................19
Description ........................................................................................................................21
Distribution and Abundance ..............................................................................................21
Habitat Associations ........................................................................................................... 26
Nesting and Roosting Habitat.........................................................................................26
Foraging Habitat ............................................................................................................27
Territoriality and Home Range ...........................................................................................27
Vocalizations ......................................................................................................................28
Interspecific Competition ...................................................................................................28
Feeding Habitats and Prey Ecology .....................................................................................28
Reproductive Biology .........................................................................................................29
Mortality Factors ................................................................................................................31
Predation ........................................................................................................................31
Starvation .......................................................................................................................31
Accidents ........................................................................................................................31
Disease and Parasites .......................................................................................................32
Population Biology ............................................................................................................. 32
Survival ..........................................................................................................................32
Reproduction .................................................................................................................33
Environmental Variation.................................................................................................33
Population Trends ...........................................................................................................33
Movements.........................................................................................................................33
Seasonal Movements. ...................................................................................................... 33
Natal Dispersal ...............................................................................................................33
Landscape Pattern and Metapopulation Structure ...............................................................34
Conclusions .......................................................................................................................34
B. B. RECO RECOVER RECO VER VERY VER Y UNIT UNITS........................................................................................................
UNIT UNIT ........................................................................................................ 36
36
United States ......................................................................................................................36
Colorado Plateau ............................................................................................................36
Southern Rocky Mountains - Colorado...........................................................................40
Southern Rocky Mountains - New Mexico......................................................................40
Upper Gila Mountains....................................................................................................44
Basin and Range - West ..................................................................................................46
Basin and Range - East ...................................................................................................46
Mexico ...............................................................................................................................49
Sierra Madre Occidental - Norte .....................................................................................49
Sierra Madre Oriental- Norte .......................................................................................... 50
Sierra Madre Occidental - Sur........................ .................................................................50
Sierra Madre Oriental - Sur.............................................................................................51
Eje Neovolcanico ............................................................................................................51
ii

Mexican Spotted Owl Recovery Plan
C. C. DEFINITIONS DEFINITIONS OF OF FOREST FOREST CO COVER CO VER TYP YP YPES YP ES ES.............................................................
ES ............................................................. 52
52
Literature Review................................................................................................................52
Ponderosa Pine ...............................................................................................................53
Mixed-conifer .................................................................................................................53
Spruce-fir .......................................................................................................................54
Other Forest Types of Interest .........................................................................................54
Chihuahua Pine..........................................................................................................54
Quaking Aspen ...........................................................................................................55
Riparian Forests ..........................................................................................................55
Plan Definitions .................................................................................................................55
Ponderosa Pine Forest .....................................................................................................55
Pine-oak Forest ...............................................................................................................55
Mixed-conifer Forest.......................................................................................................56
High-elevation Forests, Including Spruce-fir Forest .........................................................57
Quaking Aspen...............................................................................................................57
Key to Forest Types.............................................................................................................57
D. D. CONCEPTU
CONCEPTUAL CONCEPTU AL FRAME FRAMEWORK FRAME ORK FOR FOR RECO RECOVER RECO VER VERY....................................................
VER .................................................... 59
59
Ecosystem or Landscape Management ................................................................................59
Fire.................................................................................................................................60
Other Natural Disturbances ............................................................................................61
Degradation of Riparian Forests ......................................................................................65
Timber Harvest and Silvicultural Practices ..........................................................................65
Historical Perspectives ....................................................................................................65
Past Practices ..............................................................................................................65
Forest Plans ................................................................................................................66
Habitat Trends ............................................................................................................66
Data Availability .....................................................................................................66
Trends in Forest Land Base and Timber Volume ...................................................... 67
Trends in Forest Types ............................................................................................67
Trends in Size-class Distibutions .............................................................................68
Summary of Recent Habitat Trends ........................................................................68
Silvicultural Practices and Forest Management ................................................................68
Silviculture .................................................................................................................69
Even-aged Management .......................................................................................... 69
Uneven-aged Management......................................................................................70
Development and Maintenance of Stratified Mixtures .............................................71
Conclusions.................................................................................................................... 71
Grazing .............................................................................................................................. 72
Recreation .......................................................................................................................... 73
Types of Recreation ........................................................................................................ 73
Camping .................................................................................................................... 74
Hiking ....................................................................................................................... 74
Off-road Vehicles ....................................................................................................... 74
Rock Climbing ........................................................................................................ . 74
Wildlife Viewing and Photography........................................................................... . 74
Recreation Summary .................................................................................................. .74
Summary........................................................................................................................... .75
iii

PAR AR ART AR T III: III: RECO RECOVER RECO VER VERY VER
Mexican Spotted Owl Recovery Plan
A. A. DELISTING DELISTING .................................................................................................................... .................................................................................................................... 76 76
76
The Delisting Process ........................................................................................................ 76
Delisting Criteria ............................................................................................................... 76
Monitoring Population Trends ....................................................................................... 77
Other Considerations of Population Monitoring ........................................................ 79
Monitoring Habitat Trends ............................................................................................ 79
Long-term Management Plan ........................................................................................ 80
Delisting at the Recovery Unit Level .............................................................................. 80
Moderating and Regulating Threats. .......................................................................... 81
Habitat Trends Within Recovery Units ....................................................................... 81
B. B. GENERAL GENERAL APPR APPROACH
APPR CH ................................................................................................ ................................................................................................ 82
82
Assumptions and Guiding Principles.................................................................................. 82
Assumptions. ................................................................................................................. 83
Guiding Principles ......................................................................................................... 84
General Recommendations ................................................................................................ 84
Protected Areas .............................................................................................................. 84
Protected Activity Center (PAC) ................................................................................ 84
Guidelines ............................................................................................................. 84
Rationale ............................................................................................................... 89
Steep Slopes (Outside of PACs) .................................................................................. 89
Guidelines ............................................................................................................. 89
Rationale ............................................................................................................... 89
Reserved Lands .......................................................................................................... 90
Guidelines ............................................................................................................. 90
Rationale ............................................................................................................... 90
Restricted Areas ............................................................................................................. 90
Existing Conditions ................................................................................................... 91
Reference Conditions ................................................................................................. 91
Nesting and Roosting target/threshold conditions .................................................. 91
Coarse Filter .............................................................................................................. 93
Fine Filter .................................................................................................................. 94
Overriding Guidelines ........................................................................................... 94
Specific Guidelines ................................................................................................ 94
Rationale ............................................................................................................... 95
Riparian Communities............................................................................................... 95
Guidelines ............................................................................................................. 95
Rationale ............................................................................................................... 95
Other Forest and Woodland Types ................................................................................. 95
Grazing Recommendations ................................................................................................ 96
Grazing Guidelines ........................................................................................................ 96
Rationale for Grazing Guidelines ................................................................................... 97
Recreation Recommendations............................................................................................ 98
Guidelines ..................................................................................................................... 98
Recovery Unit Considerations ........................................................................................... 98
Colorado Plateau ........................................................................................................... 98
Potential Threats ........................................................................................................ 99
Southern Rocky Mountains - Colorado.......................................................................... 99
iv

Mexican Spotted Owl Recovery Plan
Potential Threats ........................................................................................................ 99
Southern Rocky Mountains - New Mexico..................................................................... 99
Potential Threats ....................................................................................................... 100
Upper Gila Mountains.................................................................................................. 100
Potential Threats ....................................................................................................... 100
Basin and Range - West ................................................................................................ 101
Potential Threats ....................................................................................................... 101
Basin and Range - East ................................................................................................. 102
Potential Threats ....................................................................................................... 102
Mexico ......................................................................................................................... 103
Potential Threats ....................................................................................................... 104
Sierra Madre Occidental - Norte ........................................................................... 104
Sierra Madre Oriental - Norte............................................................................... 104
Sierra Madre Occidental - Sur............................................................................... 104
Sierra Madre Oriental - Sur .................................................................................. 104
Eje Neovolcanico .................................................................................................. 104
C. C. MONIT MONITORING MONIT ORING PR PROCEDURES
PR OCEDURES
OCEDURES.................................................................................
OCEDURES ................................................................................. 105
105
Habitat Monitoring .......................................................................................................... 105
Macrohabitat ................................................................................................................ 105
Microhabitat ................................................................................................................ 106
Population Monitoring ..................................................................................................... 107
Target Population ......................................................................................................... 107
Sampling Units............................................................................................................. 107
Sampling Procedures..................................................................................................... 108
Stratification ............................................................................................................. 108
Selection of Quadrats ................................................................................................ 108
Sampling Within Quadrats ....................................................................................... 108
Banding Birds ........................................................................................................... 109
Statistical Analysis......................................................................................................... 109
Estimation of Capture Probability ............................................................................. 109
Estimation of Density Per Quadrat............................................................................ 110
Estimation of Density Per Stratum ............................................................................ 110
Variance Estimators ................................................................................................... 111
Cormack-Jolly-Seber Models ..................................................................................... 111
Personnel ...................................................................................................................... 111
Training .................................................................................................................... 112
Computerized Data Entry and Summarization.............................................................. 112
Costs ............................................................................................................................ 113
Potential Experiments ................................................................................................... 113
Alternative Designs for Population Monitoring ............................................................. 114
Drawing New Samples of Quadrats Each Year ........................................................... 114
Conducting Surveys Less Often than Yearly ............................................................... 115
Adaptive Sampling .................................................................................................... 115
Conclusions ..................................................................................................................... 115
D. D. A AACTIVIT
A ACTIVIT
CTIVIT CTIVITY-SP
CTIVIT -SP -SPECIFIC -SPECIFIC
ECIFIC RESEAR RESEARCH
RESEAR CH ............................................................................ ............................................................................ 116
116
Role of the Scientific Process ............................................................................................ 116
Important Ascpects of Experimental Design...................................................................... 117
Limitations in Past Research on the Mexican Spotted Owl ................................................ 118
Research Needs................................................................................................................. 118
Dispersal ...................................................................................................................... 119
v

Mexican Spotted Owl Recovery Plan
Genetics. .......................................................................................................................... 120
Habitat ............................................................................................................................. 120
Population Biology ...........................................................................................................120
Threats to Recovery .......................................................................................................... 120
Other Ecosystem Components ......................................................................................... 120
E. E. SUMMAR SUMMARY SUMMAR SUMMAR Y OF OF RECO RECOVER RECO VER VERY VER ........................................................................................ ........................................................................................ 121
121
PAR AR ART AR T IV IV: IV : RECO RECOVER RECO RECO VER VERY VER Y PL PLAN PL AN IMPLEMENT
IMPLEMENTATION
IMPLEMENT TION TION
A. A. IMPLEMENTING IMPLEMENTING L LLAWS,
L WS, REGUL REGULATIONS, REGUL TIONS, AND AND A AAUTHORITIES
A UTHORITIES ......................
...................... ...................... 124
124
Endangered Species Act .................................................................................................... 124
Section 4 ...................................................................................................................... 124
Section 5 ...................................................................................................................... 125
Section 6 ...................................................................................................................... 125
Section 7 ...................................................................................................................... 125
Section 8 ...................................................................................................................... 126
Section 9 ...................................................................................................................... 126
Section 10 .................................................................................................................... 126
National Forest Management Act...................................................................................... 126
National Environmental Policy Act ...................................................................................128
Migratory Bird Treaty Act ................................................................................................. 128
Tribal Lands ..................................................................................................................... 128
State and Private Lands ..................................................................................................... 128
Mexico ............................................................................................................................. 128
B. B. IMPLEMENT
IMPLEMENTATION IMPLEMENT
IMPLEMENT TION O OOVERSIGHT
O VERSIGHT ........................................................................... ........................................................................... 129
129
Recovery Unit Working Teams.......................................................................................... 129
Continuing Duties of the Recovery Team ......................................................................... 120
Centralized Spotted Owl Information Repository ............................................................. 130
C. C. STEPDO STEPDOWN STEPDO STEPDO WN OUTLINE OUTLINE .............................................................................................. .............................................................................................. 131
131
D. D. D. IMPLEMENT
IMPLEMENT
IMPLEMENTATION IMPLEMENT TION AND AND COST COST SCHEDULE SCHEDULE ....................................................... ....................................................... 137
137
GL GLOSSAR GL OSSAR OSSARY OSSAR ..................................................................................................................... ..................................................................................................................... 145
145
LITERA LITERATURE LITERA TURE CITED CITED ................................................................................................... ................................................................................................... 152
152
APP APPENDIX APP ENDIX A: A: The The The R RReco
R eco ecover eco er ery er y Team eam and and and Associates Associates ....................................................... ....................................................... 163 163
163
APP APPENDIX APP APPENDIX
ENDIX B: B: Schedule Schedule of of MM
Meetings MM
eetings ............................................................................. ............................................................................. 165 165
165
APP APPENDIX APP ENDIX C: C: Schedule Schedule of of F FField
F ield Visits Visits ......................................................................... ......................................................................... 166
166
APP APPENDIX APP ENDIX D: D: List List of of EE
English E nglish and and Latin Latin N NNames
N ames .......................................................... .......................................................... 167
167
APP APPENDIX APP ENDIX E: E: Agencies Agencies Agencies and and P PPersons
P ersons Commenting Commenting on on D DDraft
D raft R RReco
RR
eco ecover eco er ery ery
y P PPlan
PP
lan ............... ............... 170 170
170
vi

List List of of Tables
Tables
Mexican Spotted Owl Recovery Plan
Table able ES.1 ES.1 Overview of management categories by vegetation type for lands not
administratively reserved.................................................................................................................xi
Table able I.D.1 I.D.1 Summary of relative Mexican spotted owl population size, timber harvest threat, and fire
threat by Recovery Unit.................................................................................................................. 12
Table able II.A.1. II.A.1. Historical records and minimum numbers of Mexican spotted owls
found during planned surveys and incidental observations, reported by Recovery Unit
and land ownership .................................................................................................................. 23-24
Table able II.B.1. II.B.1. Land-ownership patterns (thousands of hectares) in Recovery Units
within the United States .................................................................................................................41
Table able II.B.2. II.B.2. Land-ownership patterns (thousands of hectares) in Recovery Units
within Mexico ................................................................................................................................50
Table able able II.D.1. II.D.1. Changes in the area (ha x 1,000 [ac x 1,000]) and distribution of
forest types from the 1960s to 1980s on commercial forest lands within Arizona
and New Mexico ............................................................................................................................67
Table able II.D.2. II.D.2. Changes in the density (trees/ha [trees/ac]) and distribution of
tree size classes from the 1960s to 1980s on commercial forest lands within Arizona
and New Mexico ............................................................................................................................68
Table able III.B.1 III.B.1 III.B.1 Target/threshold conditions for mixed-conifer and pine-oak forests
within restricted areas .....................................................................................................................92
Table able IV IV.1 IV .1 Implementation and cost schedule ..................................................................... 139-144
vii

List List List of of Figures
Figures
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e II.A.1. II.A.1. Geographic range of the spotted owl ......................................................................20
Figur igur igure igur e II.A.2. II.A.2. II.A.2. Current distribution of Mexican spotted owls in the United States
based on planned surveys and incidental observations recorded from 1990 through 1993...............22
Figur igur igure igur e II.A.3. II.A.3. Current distribution of Mexican spotted owls in Mexico based on
planned surveys and incidental observations recorded from 1990 through 1993 .............................. 25
Figur igur igure igur e II.A.4. II.A.4. Geographic variability in the food habits of Mexican spotted owls
represented as relative frequencies of (a) (a) woodrats, (b) (b) voles, (c) (c) gophers, (d) (d) birds,
(e) (e) bats, and (f (f) (f ) reptiles..................................................................................................................30
Figur igur igure igur e II.B.1. II.B.1. II.B.1. Recovery Units within the United States.................................................................37
Figur igur igure igur e II.B.2. II.B.2. Recovery Units within the Republic of Mexico ........................................................38
Figur igur igure igur e II.B.3 II.B.3 Colorado Plateau Recovery Unit.............................................................................. 39
Figur igur igur igure igur e II.B.4 II.B.4 Southern Rocky Mountains - Colorado Recovery Unit ............................................42
Figur igur igure igure
e II.B.5 II.B.5 Southern Rocky Mountains - New Mexico Recovery Unit .......................................43
Figur igur igure igur e II.B.6 II.B.6 Upper Gila Mountains Recovery Unit .....................................................................45
Figur igur igure igur e II.B.7 II.B.7 Basin and Range - West Recovery Unit ....................................................................47
Figur igur igure igur e II.B.8 II.B.8 Basin and Range - East Recovery Unit .....................................................................48
Figur igur igure igur e II.D.1 II.D.1 Historical record of number of total fires and number of
natural fires. Data from USFS Southwestern Region ......................................................................62
Figur igur igure igur e II.D.2 II.D.2 Historical record of fires over four hectares in size. Data from
USFS Southwestern Region ............................................................................................................62
Figur igur igur igure igur e II.D.3 II.D.3 Five-year running averages of area burned. Data from USFS
Southwestern Region......................................................................................................................63
Figur igur igure igur e III.A.1 III.A.1 Hypothetical curve of the statistical power to detect a trend in a population ...........78
Figur igur igure igur e III.B.1 III.B.1 Conceptualization of the Recovery Plan and needs for delisting
of the Mexican spotted owl depicting the interdependency of population
monitoring, habitat monitoring, and management recommendations .............................................83
Figur igur igure igur e III.B.2 III.B.2 Generalization of protection stratgies by forest/vegetation type ...............................85
Figur igur igure igur e III.B.3 III.B.3 Examples of protected activity center (PAC) boundaries from
the Lincoln National Forest ............................................................................................................87
viii

Volume 1/Executive Summary
INTRODUCTION
INTRODUCTION
The Mexican spotted owl was listed as a
threatened species on 15 April 1993. Two
primary reasons were cited for the listing: historical
alteration of its habitat as the result of
timber management practices, specifically the
use of even-aged silviculture, plus the threat of
these practices continuing, as provided in National
Forest Plans. The danger of catastrophic
wildfire was also cited as a potential threat for
additional habitat loss. Concomitant with the
listing of the Mexican spotted owl, a Recovery
Team was appointed by FWS Southwestern
Regional Director John Rogers to develop a
Recovery Plan. This report constitutes the
Recovery Plan for the Mexican spotted owl.
This Recovery Plan provides a basis for
management actions to be undertaken by landmanagement
agencies and Indian Tribes to
remove recognized threats and recover the
spotted owl. Primary actions will be taken by the
USDA Forest Service, USDI Bureau of Land
Management, USDI Fish and Wildlife Service,
USDI Bureau of Indian Affairs, and sovereign
American Indian Tribes. The Fish and Wildlife
Service will oversee implementation of the
Recovery Plan through its authorities under the
Endangered Species Act.
The Team made every effort to identify and
consider all sources of information in developing
this plan. Previous plans developed for the
northern spotted owl (Thomas et al. 1990, Bart
et al. 1992) and the California spotted owl
(Verner et al. 1992) were considered in the
development of this Recovery Plan. The Team
analyzed data that had not been evaluated
previously and re-analyzed data when appropriate
to ensure that information was consistent or
to address questions not considered in previous
analyses of those data.
RECOVERY RECOVERY RECOVERY GOAL
GOAL
The purpose of this Recovery Plan is to
outline the steps necessary to remove the Mexi-
EXECUTIVE EXECUTIVE SUMMARY
SUMMARY
ix
Mexican Spotted Owl Recovery Plan
can spotted owl from the list of threatened
species.
THE THE RECOVERY RECOVERY PLAN
PLAN
The Recovery Plan contains five basic
elements:
1. A recovery goal and a set of delisting
criteria that, when met, will allow the
Mexican spotted owl to be removed from
the list of threatened species.
2. Provision of three general strategies for
management that provide varying levels
of habitat protection depending on the
owl’s needs and habitat use.
3. Recommendations for population and
habitat monitoring.
4. A research program to address critical
information needs to better understand
the biology of the Mexican spotted owl
and the effects of anthropogenic activities
on the owl and its habitat.
5. Implementation procedures that
specify oversight and coordination
responsibilities.
Each of these elements is described briefly
below.
Delisting Delisting Criteria
Criteria
The primary threat to the Mexican spotted
owl leading to its listing as a threatened species
was the alteration of its habitat in Arizona and
New Mexico as the result of timber management,
specifically even-aged management.
Mexican spotted owls use a variety of habitats,
but are typically associated with multi-canopied
stands of mature mixed-conifer and ponderosa
pine-Gambel oak forests. Past logging using
even-aged shelterwood prescriptions that included
short rotations and the removal of large

volumes of timber greatly simplified stand
structures which adversely affected >300,000 ha
(800,000 ac) of spotted owl habitat (Fletcher
1990). Existing Forest Plans call for continued
use of shelterwood harvests, potentially leading
to continued loss of owl habitat. However, the
Team recognizes and is encouraged by recent
efforts to amend existing Forest Plans to deemphasize
the use of even-aged silviculture and
incorporate the management guidelines provided
within this Recovery Plan.
The range of the Mexican spotted owl was
divided into six Recovery Units in the United
States and five in Mexico. Recovery Units were
based on various factors including biotic provinces,
the spotted owl’s ecology, and management
considerations. If delisting criteria are met,
Recovery Units can be delisted separately. The
following criteria must be met for delisting to be
considered: (1) the population in the three most
populated Recovery Units must be stable or
increasing after 10 years of monitoring; (2)
scientifically-valid habitat monitoring protocols
are designed and implemented to assess (a) gross
changes in habitat quantity across the range of
the Mexican spotted owl, and (b) habitat modifications
and habitat trajectories within treated
stands; and (3) a long-term management plan is
in place to ensure appropriate management for
the spotted owl and its habitat. If these three
criteria are met, then the Mexican spotted owl
can be delisted within any Recovery Unit if
threats have been moderated or regulated, and if
habitat trends are stable or increasing.
Levels Levels of of Protection
Protection
General recommendations are proposed for
three levels of management: protected areas,
restricted areas, and other forest and woodland
types (Table ES.1). Protected areas include a 243
ha (600 ac) “Protected Activity Center” (PAC)
placed at known or historical nest and/or roost
sites, slopes >40% in mixed-conifer and pine-oak
forests that have not been harvested within the
past 20 years, and administratively reserved
lands. Harvest of trees >22.4 cm (9 inches) dbh
(diameter at breast height) is not allowed within
protected areas, but light underburning is
permitted on a case-specific basis as needed to
Volume 1/Executive Summary
x
Mexican Spotted Owl Recovery Plan
reduce fuels. Also, a fire risk-abatement program
is proposed to allow the treatments of fuels using
a combination of fuel removal and fire. This
management can be conducted initially within
10% of the PACs, after which time the effectiveness
of the program should be evaluated. Similar
management can be conducted on steep slopes,
but with no areal restrictions.
Restricted areas include ponderosa pine-
Gambel oak and mixed-conifer forests and
riparian environments. Target/threshold criteria
are provided to define the proportion of the
landscape that should be in or approaching
conditions suitable for nesting and roosting. The
remainder of the landscape should be managed
in such a way to allocate stands to ensure a
sustained provision of nest and roost habitat
through time. Broad guidelines for riparian
systems emphasize the maintenance and restoration
of riparian areas to ensure a mix of size and
age classes.
Other forest and woodland types include
ponderosa pine and spruce-fir forests, pinyonjuniper
woodlands, and aspen groves that are not
included within PACs. No specific guidelines are
proposed, but general recommendations are
given to manage these areas for landscape diversity
within natural ranges of variation.
Population Population and and Habitat Habitat Monitoring
Monitoring
The Recovery Plan provides a detailed
program to monitor spotted owl populations
and habitats. Both are key components of the
delisting criteria. Population monitoring is
restricted to the three most populated Recovery
Units because their spotted owl populations
meet sample size criteria for the monitoring
design. Further, these Recovery Units comprise
the core Mexican spotted owl population and
the Team assumes that their population status
reflects that of the entire population. The design
presented in the Recovery Plan entails the use of
mark-recapture methodology on random quadrats
to estimate key population parameters. The
objectives of the habitat monitoring are (a) to
track gross changes in habitat quality and quantity
using remote sensing technology, and (b) to
evaluate whether treatments meet the desired
goal of setting stands on trajectories to become
replacement habitat.

Table able ES.1.
ES.1. Overview of management categories by vegetation type for lands not
administratively reserved.
Volume 1/Executive Summary
Mexican Spotted Owl Recovery Plan
Vegetation egetation In n N NNest
N est S SSlope
S lope Timber imber H HHar
H ar arvest ar est est
Within ithin PP
Past PP
ast Management anagement anagement
Type ype Ar Area? Ar ea? 1 > 40% 40% 20 20 Years? ears? Categor ategor ategory ategor
Any Yes Protected
Mixed-conifer No Yes No Protected
Pine-Oak No Yes No Protected
Mixed-conifer No Yes Yes Restricted
Pine-Oak No Yes Yes Restricted
Mixed-conifer No No Restricted
Pine-Oak No No Restricted
Riparian No No Restricted
Ponderosa Pine No No Other types
Spruce-Fir No No Other types
Pinyon-Juniper No No Other types
Aspen No No Other types
Oak No No Other types
1 Refers to land contained within a protected activity center.
Activity-specific Activity-specific Research Research Program Program
Program
The Recovery Team made extensive use of
scientific data. During the process of gathering
and evaluating these data, it became evident that
additional information was needed to refine the
recovery measures. Past research efforts emphasized
inductive approaches to gather information
on basic life history needs of the spotted owl.
Although these research efforts provided some
key information, more rigorous and directed
approaches will be needed to address questions
on dispersal, genetics, habitat, populations, and
effect of management on spotted owls and other
ecosystem attributes.
Implementation Implementation Measures
Measures
Recovery Plans are not self-implementing
under the Endangered Species Act. Thus, an
implementation schedule is provided that
outlines steps needed for the execution of the
recovery measures. These implementation
guidelines include the formation of an interagency
working team for each Recovery Unit to
oversee implementation of the recovery measures
that encompass four broad areas: resource
xi
management programs, active management
actions, monitoring, and research.
CONCLUSION
CONCLUSION
The Recovery Plan is based largely on final
and preliminary results of field studies of spotted
owl habitat use, population biology, and distribution.
The Team relied on information published
in the both scientific and “gray” literature.
If data were available but unanalyzed, the Team
made every reasonable effort to conduct those
analyses. Reanalyses of data were conducted
when the Team wished to address questions not
addressed by those who collected the data. Thus,
this Recovery Plan represents the current stateof-knowledge
on the Mexican spotted owl.
The Recovery Plan recommendations are a
combination of (1) protection of both occupied
habitats and unoccupied areas approaching
characteristics of nesting habitat, and (2) implementation
of ecosystem management within
unoccupied but potential habitat. The goal is to
protect conditions and structures used by spotted
owls where they exist and set other stands on
a trajectory to grow into replacement nest
habitat or to provide conditions for foraging and

dispersal. By necessity this Plan is a hybrid
approach because the status of the Mexican
spotted owl as a threatened species requires some
level of protection until the subspecies is
delisted. These constraints modify ways and
opportunities to manage ecosystems within
landscapes where owls occur or might occur in
the future. The Plan advocates applying ecosystem
management in two slightly different ways.
Within unoccupied mixed-conifer and pine-oak
forest on

ACKNOWLEDGMENTS
ACKNOWLEDGMENTS
Mexican Spotted Owl Recovery Plan
Many people helped in the completion of this Plan. A list of people who commented on the draft
Recovery Plan is provided in Appendix E. In addition, we thank everyone who contributed valuable
time and information to the Recovery Team, and apologize for any omissions in our special thanks to
the following:
Suppor uppor upport uppor t of of the the the team team: team Nancy M. Kaufman, John G. Rogers, Jim Young, Susan MacMullin, Jamie
Rappaport-Clark (Fish and Wildlife Service [FWS] Region 2); Denver Burns (Rocky Mountain Station
[RMS], Colorado); Charles W. Cartwright, Jim Lloyd, John Kirkpatrick, Larry Henson (Forest Service
[FS] Region 3).
Providing viding viding data data to to the the team team: team Craig Allen, Mike Britten, Dick Braun, Larry Henderson, Clive
Pinnock (National Park Service [NPS]); George Alter, Cheryl Carothers, Larry Cordova, Larry Cosper,
Katherin Farr, Keith Fletcher, Heather Hollis, Patrick D. Jackson, Mike Manthei, Renee Galeano-
Popp, Danney Salas, John Shafer, Dennis Watson (FS); Mike Bogan, Cindy Ramotnik (National
Biological Service, [NBS]); Erik Brekke (Bureau of Land Management, [BLM]); Russell Duncan (SW
Field Biologists); R.J. Gutiérrez, David Olson, Mark Seamans (Humboldt State Univ. [HSU]); Charles
Johnson, Richard Reynolds (RMS); Susan Eggen-McIntosh (Southern Station New Orleans); Pat
Mehlhop (Natural Heritage Program, NM); Hildy Reiser (Holloman AFB, NM); Steve Speich (Dames
and Moore Consultants); Roger Skaggs (Glenwood, NM); Luis Tarango (Colegio De Postgraduados,
San Luis Potosi, Mexico); Jim Tress (SWCA Inc.); Dave Willey (N. Arizona Univ. [NAU]); Rick
Winslow (Navajo Fish and Wildl. Dept.).
Consultation Consultation and and and P PPresentations
P esentations esentations: esentations Cristen Allen, Don Reimer (DR Systems); Bruce Anderson,
Douglas A. Boyce, Paul Boucher, Cecelia Dargan, Don DeLorenzo, Jim Ellenwood, Leon Fager, Mary
Lou Fairweather, Leon Fisher, Keith Fletcher, Heather Hollis, Marlin Johnson, Milo Larson, Bob
Leaverton, Mike Leonard, Jim Lloyd, Mike Manthei, Chris Mehling, Terry Myers, Danney Salas, Steve
Servis, George Sheppard, Tom Skinner, Josh Taiz, Rich Teck, Borys Tkacz, Jon Verner, Dennis Watson
(FS); Bill Austin, Steve Chambers, George Devine, Jennifer Fowler-Propst, Marcos Gorreson, Sonja
Jahrsdoerfer, Michele James, Sue Linner, Britta Muiznieks, Carol Torrez (FWS); George Barrowclough
(Am. Museum of Natural Hist.); Ernie Beil, Sheridan Stone (Ft. Huachuca, AZ); Erik Brekke (BLM);
Tina Carlson (Natural Heritage Program); Mario Cirett (Ecological Center, Mexico); Martha Coleman,
Tanya Shenk (Colorado State Univ.); Gerald Craig (CO Division of Wildlife); Norris Dodd (AZ Game
and Fish Dept.); Russell Duncan (SW Field Biologists); Jeff Feen, Tim Wilhite (San Carlos Apache);
Eric Forsman (FS Pacific NW Res. Stn.); Brian Geils, John Lundquist, Richard Reynolds (RMS); R.J.
Gutiérrez, Dave Olson, Mark Seamans (HSU); Steve Haglund (Bureau of Indian Affairs); Craig Hauke
(NPS); Tod Hull, Rich VanDemark (Applied Ecosystem Management Inc.); Terry Johnson (independent
researcher); Joe Jojola (White Mtn. Apache); Norman Jojola (Mescalero Apache); Cameron
Martinez (Northern Pueblos); Marcelo Marquez, Luis Tarango (Colegio De Postgraduados, San Luis
Potosi, Mexico); John McTague (NAU); Armando Cortez Ortiz, Jose Luis Omelasde Anda (National
Institute of Statistics and Geographic Info., Mexico); Peter Stacey (Univ. of Nevada); Alejandro
Velazques (Silviculturist, Mexico); Jerry Verner (FS Pacific SW Res. Stn.); Bob Waltermire (FWS/
NBS); Sartor O. Williams, III (NM Dept. Game & Fish); Kendall Young (New Mexico State. Univ.);
Mary Price (Univ. Calif., Riverside); Carl Marti (Weber State College); Andy Carey (FS Pacific NW
Res. Stn.).
xiii

xiv
Mexican Spotted Owl Recovery Plan
Conducting Conducting FF
Field FF
ield ield Trips ips ips: ips Bruce Anderson, Don DeLorenzo, Heather Green, Dave Nelson,
Danney Salas, Steve Servis (FS); Russell Duncan (SW Field Biologists); Joe Jojola (White Mtn.
Apache); San Carlos Apache Tribe, White Mountain Apache Tribe (providing the team access to their
lands); Steve Speich (Dames and Moore Consultants); Sheridan Stone (Ft. Huachuca, AZ); Luis
Tarango (Colegio De Postgraduados, San Luis Potosi, Mexico).
Gather ather athering ather ing and and and Analyzing Analyzing D DData
D ata ata: ata Damon Brown, Charlotte Corbett, Laura Duncan, Jill Dwyer,
Jeff Jenness, Rudy King, Sharon Masek, Mike Nelson, Janie Sandoval, Peter Scott, Wayne Shepperd,
Doug Spaeth, Mike Stanghellini, Gerry Wildeman, Randy Wilson, Rick Winslow, Karen Yarnell
(RMS); Martha Coleman, Kevin Kalin (CSU); Susan DeRosier, Earl Hill, Karen Holmstrom, Rich
Teck (FS); Susan Eggen-McIntosh (FS Southern Stn., New Orleans); Bob Waltermire, Barb White
(FWS/BS); Dave Willey (NAU).
Logistical Logistical S SSuppor
S uppor upport: uppor Bekki King, Karen Montano (FWS); Kim Ross (RMS).

Mexican Spotted Owl Recovery Plan
Volume I

Recovery Plan Development
Volume I, Part I

The USDI Fish and Wildlife Service (FWS)
added the Mexican spotted owl to the List of
Threatened and Endangered Wildlife (50 CFR
17.11) as a threatened species, effective on 15
April 1993. Section 4(f)(1) of the Endangered
Species Act of 1973, as amended (Act) (16
U.S.C. 1531), requires the Secretary of the
Interior (usually delegated to the Director of the
FWS) to “...develop and implement (recovery)
plans for the conservation of endangered species
and threatened species...unless he finds that such
a plan will not promote the conservation of the
species.”
To develop scientifically credible recovery
plans for listed species, the FWS may appoint
recovery teams comprised of scientists and
resource specialists with expertise either on the
species being considered or with other relevant
expertise. In the case of the Mexican spotted
owl, the FWS appointed the Mexican Spotted
Owl Recovery Team (Recovery Team). A list of
Recovery Team members and their areas of
expertise can be found in Appendix A. A chronology
of Recovery Team activities is provided in
Appendices B and C.
Recovery teams present recovery plans to the
FWS as their recommendation on the steps
necessary to remove a species from the List of
Threatened and Endangered Wildlife and Plants.
Removal from the list, or “delisting,” means the
species is no longer in need of protection under
the Act and is therefore considered “recovered.”
If deemed acceptable, the Director of the FWS
Region assigned the lead for that species approves
the plan.
The FWS, pursuant to requirements under
section 4(f)(4) of the Act, published a Notice of
Availability of the Draft Mexican Spotted Owl
Recovery Plan in the Federal Register on March
27, 1995 (60 FR 15787). In addition to this
general solicitation for information and public
comment, the FWS sent copies of the draft
Recovery Plan to numerous Federal and State
agencies, Indian Tribes, county governments,
environmental and industry groups, and others
who had expressed interest in the Mexican
spotted owl. Finally, specific professional organizations
and individuals were asked to provide
Volume I/Part I
A. A. RECOVERY RECOVERY RECOVERY PLANNING
PLANNING
1
Mexican Spotted Owl Recovery Plan
peer review of either the entire document or
portions treating subjects within their specific
areas of expertise. A list of reviewers is provided
in Appendix E.
Recovery plans are neither self-implementing
nor legally binding. Rather, approved recovery
plans effectively constitute FWS policy on that
listed species or group of species, thereby guiding
the Service in conducting various processes
required under the Act, such as section 7 consultation,
conservation planning under section 10,
and other procedures. In most cases, recovery
plans are followed by other Federal agencies in
compliance with the mandate under sections
2(c)(1) and 7(a)(1) of the Act to utilize their
authorities in carrying out programs for the
conservation of endangered and threatened
species. In addition, State and local governments
usually follow the recommendations of recovery
plans in their species conservation efforts.
Section 4(f)(1)(B) of the Act specifies the
contents of a recovery plan:
“(i) a description of such site-specific
management actions as may be necessary
to achieve the plan’s goal for the
conservation and survival of the
species” (III.B);
“(ii) objective, measurable criteria which,
when met, would result in a
determination...that the species be
removed from the list” (III.A);
“(iii) estimates of the time required and the
cost to carry out those measures
needed to achieve the plan’s goal and
to achieve intermediate steps toward
that goal” (IV.C and IV.D).

The Mexican spotted owl is one of three
spotted owl subspecies (see II.A). Under section
3 of the Act, the term “species” includes “...any
subspecies of fish or wildlife...”. Although the
Mexican spotted owl is a subspecies, it is sometimes
referred to as a “species” in this document
when discussed in the context of the Act or other
laws and regulations. An “endangered species” is
defined under the Act as “...any species which is
in danger of becoming extinct throughout all or
a significant portion of its range....” A threatened
species is one “...which is likely to become
an endangered species in the foreseeable future
throughout all or a significant portion of its
range.” Section 4 (A)(1) of the Act lists five
factors that can, either singly or collectively,
result in listing as endangered or threatened:
“(A) the present or threatened destruction,
modification, or curtailment of its
habitat or range;
(B) overutilization for commercial, recreational,
scientific, or educational
purposes;
(C) disease or predation;
(D) the inadequacy of existing regulatory
mechanisms;
(E) other natural or man-made factors
affecting its continued existence.”
The final rule listing the Mexican spotted
owl as a threatened species (final rule) (58 FR
14248) provides a detailed discussion of the
primary factors (A and D) leading to the determination
of threatened status. It should be noted
that the Recovery Team summarizes the final
rule here for information purposes only. The
Recovery Team’s assessment of the current
situation with regard to the subspecies’ status
and threats is reflected in Part III. The following
briefly summarizes the factors leading to the
species’ listing, as discussed in the final rule:
Volume I/Part I
B. B. LISTING
LISTING
2
Mexican Spotted Owl Recovery Plan
THE THE PRESENT PRESENT OR OR THREATENED
THREATENED
THREATENED
DESTRUCTION, DESTRUCTION, MODIFICATION,
MODIFICATION,
OR OR CURTAILMENT CURTAILMENT CURTAILMENT OF OF ITS
ITS
HABITAT HABITAT OR OR OR RANGE RANGE
RANGE
Past, current, and future timber-harvest
practices in the Southwestern Region (Region 3)
of the USDA Forest Service (FS) were cited as
the primary factors leading to listing the Mexican
spotted owl as a threatened species. The final
rule stated that the Southwestern Region of the
FS managed timber primarily under a
shelterwood harvest regime. This harvest method
produces even-aged stands rather than the
uneven-aged, multi-layered stands most often
used by Mexican spotted owls for nesting and
roosting. In addition, the shelterwood silvicultural
system calls for even-aged conditions in
perpetuity. Thus, stands already changed from
“suitable” to “capable” would not be allowed to
return to a “suitable” condition; and acreage
slated for future harvest will be similarly rendered
perpetually unsuitable for Mexican spotted
owl nesting and roosting.
The final rule stated that “...significant
portions of spotted owl habitat have been lost or
modified,” and cited Fletcher (1990) in estimating
that 420,000 ha (1,037,000 ac) of habitat
were converted from “suitable” to “capable.” Of
this, about 78.7%, or 330,000 ha (816,000 ac),
was a result of human activities, whereas the
remainder was converted naturally, primarily by
wildfire. According to the final rule, forest plans
in the FS Region 3 allowed for up to 95% of
commercial forest (59% of suitable spotted owl
habitat) to be managed under a shelterwood
system. The loss of lower- and middle-level
riparian habitat plus habitat lost to recreation
developments were also cited in the final rule as
factors in habitat loss.

OVERUTILIZATION OVERUTILIZATION FOR
FOR
COMMERCIAL, COMMERCIAL, RECREATIONAL,
RECREATIONAL,
RECREATIONAL,
SCIENTIFIC, SCIENTIFIC, OR OR EDUCATIONAL
EDUCATIONAL
PURPOSES
PURPOSES
The final rule stated that scientific research
has the greatest potential for overutilization of
the Mexican spotted owl, whereas birding,
educational field trips, and agency “show me”
trips are likely to increase as the owl becomes
better known. The effects of these activities,
either chronically or acutely, are unknown.
Volume I/Part I
DISEASE DISEASE OR OR PREDATION
PREDATION
The final rule stated that great horned owls
and other raptors are predators of Mexican
spotted owls. It also implied that forest management
created ecotones favored by great horned
owls, thus creating an increased likelihood of
contact between the two species.
3
Mexican Spotted Owl Recovery Plan
INADEQUACY INADEQUACY OF OF EXISTING
EXISTING
REGULATORY REGULATORY MECHANISMS
MECHANISMS
MECHANISMS
The final rule discussed various Federal and
State laws and agency management policies,
concluding that existing regulatory mechanisms
were inadequate to protect the Mexican spotted
owl. For further discussion on extant regulatory
mechanisms, refer to Part IV.
OTHER OTHER NATURAL NATURAL OR OR MANMADE
MANMADE
FACTORS FACTORS AFFECTING AFFECTING ITS
ITS
CONTINUED CONTINUED EXISTENCE
EXISTENCE
The final rule cited wildfires as a past and
future threat to spotted owl habitat. The potential
for increasing malicious and accidental
anthropogenic harm to the species was also cited
as a possible threat. In addition, the final rule
recognized the potential for the barred owl to
expand its range into that of the Mexican spotted
owl, resulting in possible competition and/or
hybridization. It was speculated that habitat
fragmentation may encourage and hasten this
expansion.

Volume I/Part I
C. C. PAST PAST AND AND CURRENT CURRENT MANAGEMENT
MANAGEMENT
OF OF THE THE MEXICAN MEXICAN SPOTTED SPOTTED OWL
OWL
Prior to the proposed listing of the Mexican
spotted owl, some Federal agencies and involved
States had conferred special status on the subspecies
(e.g., State “threatened,” FS “sensitive,”
FWS “candidate”) in recognition of its rarity,
habitat preferences and threats to those habitat
types, and/or need of special management
considerations. This section summarizes the
special status assigned to the subspecies and the
resulting conservation efforts.
FISH FISH AND AND WILDLIFE WILDLIFE SERVICE
SERVICE
The FWS listed the entire spotted owl
species as a Category-2 candidate in its 6 January
1989 Notice of Review (54 FR 554). Category-2
candidates are those species that the FWS
believes may qualify for listing as threatened or
endangered but for which insufficient information
is available to support the required rulemaking
process. The northern subspecies was
listed as threatened in 1990; the California and
Mexican subspecies remained in Category-2
candidate status.
The Mexican spotted owl was proposed for
listing as a threatened species on 4 November
1991 (56 FR 56344) as a result of a status review
prompted by a petition to list the subspecies.
Following publication of the listing proposal, the
FWS attempted to develop a conservation
agreement with involved Federal agencies to
conserve the Mexican spotted owl. This effort
was unsuccessful, so the final rule was published
on 16 March 1993 (58 CFR 14248). Critical
habitat was not determinable at the time of
listing.
Since the listing of the subspecies, the FWS
has been conducting the processes associated
with listed species under the Act, such as section
7 consultation on Federal actions that may affect
the subspecies, issuance of research permits
under Section 10, and recovery planning under
section 4, including funding of several research
projects.
Two petitions to delist the species have been
reviewed by the FWS. In both cases, delisting
was determined to be “not warranted” because
4
Mexican Spotted Owl Recovery Plan
the petitions failed to present substantial scientific
and commercial information to support
their assertion that the species should be
delisted. Notices of those findings, including
discussions of the issues raised in the petitions,
were published in the Federal Register on 23
September 1993 (58 FR 49467) and 1 April
1994 (59 FR 15361).
The FWS proposed critical habitat for the
Mexican spotted owl on 7 December 1994 (59
FR 63162), and published the final critical
habitat rule on 6 June 1995 (60 FR 29914).
Since that time, the FWS has been in consultation
with action agencies on the effects of
proposed and ongoing actions on critical habitat.
FOREST FOREST FOREST SERVICE
SERVICE
The primary administrator of lands supporting
Mexican spotted owls in the United States is
the FS. Most spotted owls have been found
within FS Region 3 (including 11 National
Forests in Arizona and New Mexico). The Rocky
Mountain (Region 2, including two National
Forests in Colorado) and Intermountain (Region
4, including three National Forests in Utah)
Regions support fewer spotted owls.
Forest Forest Service Service Southwestern Southwestern Region
Region
(Region (Region 3)
3)
Prior to the listing of the Mexican spotted
owl, FS Region 3 issued detailed guidelines for
its management. Those guidelines were issued as
Interim Directive Number 1 (ID No. 1) in June
1989, then revised and reissued as ID No. 2
approximately one year later. Although ID No. 2
expired in December 1991, FS Region 3 has
continued managing under those guidelines.
Interim Directive Number 2 guidelines
required establishing management territories
around all nesting and roosting spotted owls, as
well as territorial owls detected at night for
which daytime locations were not recorded. All
management territories except those on the
Lincoln and Gila National Forests had a 182-ha

(450 ac) core area surrounded by 627 ha (1,550
ac) of the “best available” habitat, extending the
area to 809 ha (2,000 ac) per management
territory. On the Lincoln and Gila National
Forests, the 182-ha (450 ac) cores were augmented
by an additional 425 ha (1,050 ac) of
habitat, for a total management territory size of
607 ha (1,500 ac).
Except for road construction, habitat degradation
was not allowed within management
territory cores. In the remainder of the management
territory management activities, including
timber harvest, were limited to 209-314 ha
(516-775 ac). The FS guidelines provided no
protection for unoccupied habitat except in
wilderness areas and administratively restricted
lands.
The FS Region 3 has been in the process of
amending forest plans through the National
Environmental Policy Act (NEPA) process to
incorporate the management recommendations
contained in this Recovery Plan. The Recovery
Team commends that effort.
Forest Forest Forest Service Service Rocky Rocky Mountain Mountain Region
Region
(Region (Region (Region 2)
2)
Region 2 of the FS formed a task force in
1992 to begin developing management guidelines
for the Mexican spotted owl. These management
guidelines are still in draft form and
have not been formally approved and adopted by
FS Region 2. However, management activities
continue to be examined on a case-by-case basis,
and ID No. 2 may be used as a general guideline.
Forest Forest Service Service Service Intermountain Intermountain Region
Region
(Region (Region (Region 4)
4)
Prior to the listing of the Mexican spotted
owl, biologists from FS Region 4 and Utah’s
other land and wildlife management agencies,
plus owl researchers, formed the Utah Mexican
Spotted Owl Working Group (Working Group).
The Working Group meets annually to identify
and address issues pertaining to the management
and conservation of Mexican spotted owls in
Utah (Kate Grandison, FS, Cedar City, UT, pers.
comm.). The Utah Mexican Spotted Owl
Technical Team (Technical Team) was formed by
Volume I/Part I
5
Mexican Spotted Owl Recovery Plan
the Working Group to focus on spotted owl
issues such as (1) potential impacts to Mexican
spotted owls in southern Utah; (2) current
research and future research needs and priorities;
(3) inventory and monitoring protocols; (4)
management suggestions suitable for application
by all land management agencies in southern
Utah; and (5) dissemination of information
from the Working Group and Technical Team to
management and administrative levels. The goals
of the Technical Team, which is composed of
biologists from the FWS, FS, USDI Bureau of
Land Management (BLM), USDI National Park
Service (NPS), Utah Division of Wildlife Resources
(UDWR), and a researcher/technical
consultant, are to provide land and wildlife
managers with the information necessary to
ensure the protection of Mexican spotted owls
and to suggest strategies for managing spotted
owl habitat in Utah.
The Technical Team developed “Suggestions
for Management of the Mexican Spotted Owl in
Utah.” These suggestions were sent to line
officers for approval on 5 August 1994. Management
territories on the Manti-LaSal National
Forest were established using these suggestions,
although ID No. 2 has also been adopted by
Region 4. Interim Directive No. 2 was modified
in March 1994 in Region 4 to change the survey
protocol to include only potential breeding
habitat in canyon areas below 2,590 m (8,500
ft).
According to the suggestions, management
territory size should be 1,330 ha (3,350 ac) with
355-ha (875 ac) core areas of canyon habitat. In
addition, a 0.8-km (0.5 mi) protection area
centered on the nest site was established to
protect the nest stand and surrounding areas.
Habitat degradation is not allowed in the management
territory areas. A “potential dispersal
area” extends 58 km (35.8 mi) beyond the
perimeter of the management territory. This area
can be used for timber harvest, but post-harvest
conditions must meet a reasonable facsimile of
the 50-11-40 dispersal rule developed by Thomas
et al. (1990). Forest Service Region 4
continues to manage under ID No. 2, with the
above modifications, except where superseded by
the “Suggestions for Management of Mexican
Spotted Owls in Utah.”

OTHER OTHER OTHER FEDERAL FEDERAL AGENCIES
AGENCIES
National National Park Park Service
Service
Several NPS-administered units are known
to support Mexican spotted owls, including
Zion, Capitol Reef, and Canyonlands National
Parks plus Glen Canyon National Recreation
Area in Utah; Mesa Verde National Monument
in Colorado; Grand Canyon National Park plus
Saguaro, Walnut Canyon, and Chiricahua
National Monuments in Arizona; Bandelier
National Monument in New Mexico; and
Guadalupe Mountains National Park in Texas.
The National Park Service Organic Act
protects all wildlife on National Parks and
Monuments. However, no specific management
guidelines are in place for Mexican spotted owls,
and the effectiveness of applying general laws
and policies for spotted owls is difficult to
evaluate.
Bureau Bureau of of Land Land Land Management
Management
The BLM has developed management
policies specifically for the Mexican spotted owl
in Colorado and New Mexico. The Colorado
guidelines state that “...in areas with a confirmed
nest or roost site, surface management activities
will be limited and will be determined on a caseby-case
basis to allow as much flexibility as
possible outside of the core area.” The BLM in
Colorado has management guidelines for oil and
gas development where Mexican spotted owls are
known to occur. No surface occupancy is allowed
within 0.4 km (0.25 mi) of a nest or roost
site, and restrictions on other associated activities
apply between 1 February and 31 July. Spotted
owl management policy by the BLM in New
Mexico establishes and preserves cores of habitat
wherever the owl is found. The BLM determines
the size of the cores on a case-by-case basis.
The BLM in Colorado follows the survey
techniques of the FS Region 3 spotted owl
protocol. Management territories have not been
designated for known birds. Surveys are conducted
in areas of potential habitat where
projects are planned that may be in conflict with
spotted owl management.
Volume I/Part I
6
Mexican Spotted Owl Recovery Plan
The BLM in Utah has no specific internal
guidelines on management practices for Mexican
spotted owls. However, agency personnel did
participate in producing “Suggestions for the
Management of Mexican Spotted Owls in
Utah.” The BLM will incorporate management
prescriptions for the Mexican spotted owl and its
potential habitat into resource management
plans as they are updated over the next several
years.
The BLM in Arizona has no specific guidelines
for managing Mexican spotted owls.
However, the standard BLM procedure for
assessing impacts on threatened or endangered
species will be followed for projects proposed in
spotted owl habitat. Guidelines for protecting
the owl or its habitat would then be developed
on a site-specific basis (Ted Corderey, BLM,
Endangered Species Coordinator, Phoenix
Office, pers. comm.).
Department Department of of Defense Defense
Defense
The Fort Huachuca Military Reservation
(Post) in southeastern Arizona is the only military
land known to support nesting Mexican
spotted owls. On the Post, military activity in
spotted owl habitat is generally confined to
various foot maneuvers, although the Army is
considering expanding some tank maneuvers
into higher elevations where the owl occurs
(Sheridan Stone, Fort Huachuca Military Reservation,
pers. comm.). One spotted owl site has
been popular with birders for a number of years,
but the effect of this activity is unknown. The
Army also considers wildfire to be a potential
threat and assesses the possibility of wildfire
ignition when designing military activities on
the Post.
Wintering Mexican spotted owls have been
found on Fort Carson, near Colorado Springs,
Colorado, and breeding owls are present on the
Fremont Military Operating Area, which includes
FS and BLM lands designated for conducting
military maneuvers. Finally, low-level
military air operations in some areas have been
identified as actions that may affect Mexican
spotted owls. Such operations are likely to
increase in the next several years, and the Department
of Defense is currently funding studies

of the effects of these activities on spotted owls
(M. Hildegard Reiser, Holoman Air Force Base,
pers. comm.).
Arizona
Arizona
Volume I/Part I
STATES
STATES
The Mexican spotted owl is listed as “threatened”
on the list of “Threatened Native Wildlife
in Arizona” (Arizona Game and Fish Department
1988). The Arizona Game and Fish
Department has authority to manage wildlife
under provisions of Arizona Revised Statute 17,
the goal of which is to maintain State’s natural
biotic diversity by listing and protecting threatened
and endangered species. “Threatened”
species is defined as “...those species or subspecies
whose continued presence in Arizona could
be in jeopardy in the near future. Serious threats
have been identified and populations are (a)
lower than they were historically or (b) extremely
local and small.”
Threatened status provides no special protection
to species, although it does provide a
mechanism through which the state can allocate
Heritage Program grants to fund research for
specially designated species. However, general
Arizona wildlife rules make it unlawful “...unless
otherwise prescribed...for a person to...take,
possess, transport, buy, sell or offer or expose for
sale wildlife, except as expressly permitted ....”
New New Mexico
Mexico
The State of New Mexico confers no special
status on spotted owls. However, New Mexico
Statute 17-2-14 makes it unlawful “...for any
person to take, possess, trap or ensnare, or in any
manner to injure, maim or destroy birds of the
order Strigiformes.” However, permits may be
obtained to take owls for purposes of Indian
religion, scientific study, or falconry. In addition,
persons who commercially raise poultry or game
birds may legally kill any owl that has killed their
stock.
7
Colorado Colorado
Colorado
Mexican Spotted Owl Recovery Plan
The Mexican spotted owl was listed as
threatened by the Colorado Division of Wildlife
(CDOW) in 1993. “Threatened” wildlife is
defined as “...any species or subspecies of wildlife
which, as determined by the Colorado Wildlife
Commission, is not in immediate jeopardy of
extinction but is vulnerable because it exists in
such small numbers or is so extremely restricted
throughout all or a significant portion of its
range that it may become endangered.” Threatened
status protects wildlife species by making
it unlawful “...for any person to take, possess,
transport, export, process, sell or offer for
sale...any species or subspecies of [threatened]
wildlife....” In addition, the CDOW is legislatively
mandated to “...establish such programs
including acquisition of land...as are deemed
necessary for management of...threatened
species.” An interagency working group
coordinates spotted owl inventories throughout
Colorado.
Utah Utah
Utah
The UDWR included the Mexican spotted
owl as a sensitive species on its 1987 Native Utah
Wildlife Species of Special Concern list (UDWR
1987). “Sensitive” wildlife is defined as “...any
wildlife species which, although still occurring in
numbers adequate for survival, whose population
has been greatly depleted, is declining in numbers,
distribution, and/or habitat (S1); or occurs
in limited areas and/or numbers due to a restricted
or specialized habitat (S2).” A management
program, including protection or enhancement,
is needed for these sensitive species.
The owl’s status was elevated to “Threatened”
in the revised draft list in 1992 (UDWR
1992). According to UDWR definition, “threatened”
species include “...any wildlife species,
subspecies, or population which is likely to
become an endangered species within the foreseeable
future throughout all or a significant
portion of its range in Utah or the world.”
Both sensitive and threatened species receive
“protected” status under Utah’s wildlife codes.
For species under protected status, “...[A] person

may not take...protected wildlife or their parts;
an occupied nest of protected wildlife; or an
egg of protected wildlife.” Nor may a person
“...transport,...sell or purchase...or possess
protected wildlife or their parts.”
Texas
Texas
Few Mexican spotted owls are documented
for Texas, and most of the location records are in
Guadalupe National Park. Thus, the State of
Texas has no spotted owl program. However,
Texas Parks and Wildlife Code Section 64.002
provides protection for nongame birds by
prohibiting killing, trapping, transportation,
possession of parts, and the like. Destruction of
eggs and nests of nongame birds is also prohibited.
Volume I/Part I
TRIBES
TRIBES
Tribal beliefs and philosophies guide resource
management on Tribal lands. Several
Tribes consider owls a bad omen; however, Tribal
beliefs also dictate that all living creatures are
essential parts of nature and, as such, they are
revered and protected. For example, the Elders
Council of San Carlos Apache Tribe expressed
the traditional view that owls and their homes
should not be disturbed.
Mexican spotted owl habitat or potential
habitat exists on 10 Indian reservations in the
Southwest. Eight of the Tribes have conducted
spotted owl surveys, and five Tribes have located
spotted owls on their lands. Two other Tribes
have historical spotted owl records.
Reservations were established for the benefit
of the Tribes and their members. Tribal lands are
held in “trust” by the Federal Government. They
are not considered public lands or part of the
public domain. Tribes are sovereign governments
with management authority over wildlife and
other Tribal land resources. Many Tribes maintain
professionally staffed wildlife and natural
resources management programs to ensure
prudent management and protection of tribal
resources, including threatened and endangered
species.
8
Mexican Spotted Owl Recovery Plan
The FWS is aware of spotted owl conservation
efforts on five Indian reservations: the
Mescalero Apache, Fort Apache, San Carlos
Apache, Jicarilla Apache, and Navajo Nation.
Mescalero Mescalero Mescalero Apache Apache Tribe
Tribe
The Mescalero Apache Tribe in New Mexico
actively manages their forest while managing for
all federally listed or proposed threatened or
endangered species that may exist on the reservation,
including the Mexican spotted owl. This is
accomplished through developing strategies for
identifying and managing habitat determined by
the Tribe to be necessary to ensure protection.
The Mescalero has been working with the FWS
in development of a conservation strategy for the
subspecies on reservation lands.
White White Mountain Mountain Mountain Apache Apache Tribe
Tribe
The Tribe recently developed a conservation
plan for Mexican spotted owls on the reservation.
Areas containing spotted owls are placed in
one of two land-management categories, termed
Designated Management Areas (DMAs). Areas
supporting “clusters” of four or more territories
are considered “Category-1” DMAs. In these
areas, spotted owl habitat concerns drive management
prescriptions; timber harvest is a
secondary objective. Category-1 DMAs range
from about 2,430-4,050 ha (6,000-10,000 ac),
and contain 57% of known spotted owl sites on
the reservation.
“Category-2” DMAs include areas supporting
1-3 owl territories. Habitat outside the
territories is managed only secondarily for
spotted owls, with other resource objectives
given priority. No timber harvest is allowed in
30-ha (75 ac) patches around owl activity centers.
A seasonal restriction on potentially disturbing
activities is provided in a 202-ha (500 ac)
area, and timber prescriptions within this area
should be designed to improve habitat integrity.
The Tribe continues to survey their lands for
spotted owls. If more owl sites are detected,
Category-1 and Category-2 DMAs may be
established upon approval by the Tribal Council.

San San Carlos Carlos Apache Apache Tribe
Tribe
Spotted owl surveys on the San Carlos
Apache Reservation have been conducted according
to the FS Region 3 Mexican Spotted
Owl Inventory Protocol. Mexican spotted owl
habitat has been identified and delineated
throughout the reservation. A joint Tribal/
Bureau of Indian Affairs interdisciplinary team
evaluates effects of actions on spotted owls. Any
potential impact on spotted owls or owl habitat
is deferred until compliance with the Act and
associated regulations is attained.
Preliminary discussions between the San
Carlos Apache and the FWS have taken place
regarding development of specific spotted owl
management guidelines. Approximately 90% of
tribally identified nesting, roosting, and foraging
habitats are on lands inoperable for timber
harvest and therefore are not in the commercial
timber base.
Jicarilla Jicarilla Jicarilla Apache Apache Apache Tribe
Tribe
The Jicarilla Apache Tribe has developed a
spotted owl conservation plan, approved by the
Jicarilla Tribal Council and accepted by the
FWS. No resident owls have been detected to
date on the reservation; however, in the event
resident owls are detected, the Tribe has proposed
to designate a 405-ha (1,000 ac) management
territory. Uneven-aged timber management
will be allowed to continue in all but 40 ha
(100 ac) of the territory. In the absence of
confirmed resident owls, all mixed-conifer stands
of 10 ha (25 ac) or greater are treated as roosting/nesting
sites, and timber harvest will not be
allowed. A seasonal restriction around any active
nest sites that are found is also proposed.
Navajo Navajo Nation
Nation
Mexican spotted owl management on the
Navajo Nation, and particularly on the Navajo
Nation Commercial Forest, currently adheres to
FS Region 3’s ID No. 2. The FS Region 3
Mexican Spotted Owl Inventory Protocol is
followed for all timber sales on the commercial
forest and for any project or disturbance, on or
Volume I/Part I
9
Mexican Spotted Owl Recovery Plan
off the commercial forest, that may impact
spotted owls. The current Navajo spotted owl
inventory program is limited to areas where
timber sales or other projects are planned.
The Navajo Nation is developing a multispecies
conservation plan, including management
guidelines for spotted owl conservation, in
conjunction with their 10-year plan for managing
commercial forest. Upon completion of the
multi-species conservation plan, the Navajo
Nation may apply to the FWS for a section
10(a)(1)(B) permit, which will allow limited
incidental take to occur provided an adequate
habitat conservation plan is implemented.
MEXICO MEXICO
MEXICO
The Mexican spotted owl is listed as a
threatened species under Mexico’s Official
Mexican Norm (NOM) (NOM-059-ECOL-
1994). Threatened species are defined as those
which could face danger of extinction if the
conditions that cause deterioration or modification
of their habitats, or decline of their populations,
prevail.
Species listed under NOM are afforded
certain protections:
1. Possession, use, or derivation of profit
from live wildlife or plants, whether
originating in captivity or in the wild, are
prohibited.
2. Use and exploitation of the habitats of
listed species are prohibited in some
States.
Some use of threatened species is allowed for
scientific and recovery purposes. For example,
specimens and their parts, products, and byproducts
can be removed from their natural
environment for scientific purposes under
permits issued by legal authorities, with the
understanding that specimens or their parts
cannot be used for commercial purposes. In
addition, specimens can be removed from the
wild for the purpose of captive breeding upon
approval of the Mexican government.
Under NOM, recovery plans have been
prepared for sea turtles and the monarch butter-

fly. The Government and other institutions have
shown interest in the conservation of other
species such as manatees, yellow-headed parrots,
and Mexican spotted owls, but currently no
recovery plans are in place for these species.
Social, economic, and political systems differ
in Mexico from those in the U.S. Concomitantly,
land ownership patterns differ and influence
natural resource management. Mexican
lands are classified into three types of tenancy:
1. Federal lands include all lands administered
under Federal Government institutions.
Federal lands include protected
natural areas such as Reserves of the
Biosphere, National Parks, and Areas of
Protection of Natural Resources. Protected
natural areas comprise 3% of the
total area of Mexico’s five recovery units.
Volume I/Part I
10
Mexican Spotted Owl Recovery Plan
2. Ejidal lands are allotted by the Mexican
Government to a person or community
for agriculture, forestry, mining, and
other uses. Thus, lands within ejidos are
intensively managed for natural resource
use. Ejidos comprise approximately
17.5% of the area within the Mexican
recovery units.
3. Private lands are possessed under a
“certificate of inaffectability.” Any
protection afforded these lands is at the
discretion of the landowner. Approximately
79.5% of the Mexican recovery
units is comprised of private land.

This section describes various considerations,
other than the basic biology of the
Mexican spotted owl, that were integral in
development of this Recovery Plan.
Volume I/Part I
D. D. CONSIDERATIONS CONSIDERATIONS IN
IN
RECOVERY RECOVERY PLAN PLAN DEVELOPMENT
DEVELOPMENT
RECOVERY RECOVERY UNITS
UNITS
The Mexican spotted owl is a widespread
subspecies that occurs in a wide variety of
habitats (see Part II). In addition, the threats
faced by the subspecies, the management regimes
employed by various agencies and in each
country, and the protective mechanisms available
in different portions of the subspecies’ range are
variable. Finally, spotted owl densities, food
habits, degree of isolation, and other aspects of
the subspecies’ biology differ somewhat among
portions of its range. For these reasons, the
Recovery Team partitioned the Mexican spotted
owl range into distinct recovery units. Six
recovery units were designated in the United
States: Colorado Plateau, Southern Rocky
Mountains - Colorado, Southern Rocky Mountains
- New Mexico, Upper Gila Mountains,
Basin and Range - West, and Basin and Range -
East (Figs. II.B.1 and II.B.3–II.B.8). Five recovery
units were established in Mexico: Sierra
Madre Occidental - Norte, Sierra Madre Occidental
- Sur, Sierra Madre Oriental - Norte,
Sierra Madre Oriental - Sur, and Eje
Neovolcanico (Figs. II.B.2). For a complete
description of the recovery units and the bases
for their designation see II.B.
Whereas some management recommendations
apply to the subspecies rangewide, delineating
recovery units allowed specific recommendations
to be prioritized appropriately within
each portion of the subspecies’ range. In addition,
some criteria for delisting the subspecies
apply at the recovery-unit level. This approach
allows delisting of the Mexican spotted owl by
recovery unit when certain rangewide population
and habitat criteria are met and when regional
management plans or other sufficient regulatory
mechanisms are implemented.
11
Mexican Spotted Owl Recovery Plan
THE THE CURRENT CURRENT SITUATION
SITUATION
In developing this Recovery Plan, the Recovery
Team considered various aspects of the
current spotted owl population, habitat, and
threats. Two salient points emerged. First, the
Recovery Team assumes that the current population
size and distribution are adequate for
providing a reference point for assessing future
changes in the population, since no undisputable
evidence is available indicating that the population
is declining or is significantly below historical
levels. This is a critical assumption that must
be tested through the population monitoring
required by this Recovery Plan. If the monitoring
data demonstrate that the population is
stable or increasing, the assumption of adequate
population size will be validated. Conversely, if
monitoring data show a decreasing population,
the situation will need to be reexamined and
corrective measures must be developed. Thus,
the population and habitat monitoring requirements
are essential parts of this Recovery Plan; if
these monitoring efforts are not conducted, the
management recommendations provided herein
cannot stand alone.
A second consideration involves variations in
both spotted owl densities and threats faced
throughout the subspecies’ range. Spotted owl
densities are greatest in the center of the subspecies’
range and they decrease toward the range
periphery. In addition, the main threats identified
during the listing process were forestry
practices and wildfire risk, both of which vary
across the subspecies’ range. Table I.D.1. illustrates
the Recovery Team’s appraisal.
The Upper Gila Mountains, Basin and
Range - West, and Basin and Range - East
Recovery Units have significant owl populations
with the potential of being seriously impacted by
fire and/or forestry practices (Table I.D.1). This
conclusion does not imply that the other recovery
units are not important, but leads to the
recommendations that (1) recovery efforts
concentrate on recovery units with the highest
owl populations and where significant threats

exist; (2) management within recovery units
should emphasize alleviating the greatest threats;
and (3) the management recommendations in
Part III should be tailored to the owl population
and the threats existing in the specific area under
analysis.
The Recovery Team believes the risk of
extirpation of Mexican spotted owls under the
near-term management recommendations is low.
This belief is based on two points:
1. Implementation of the management
recommendations within this Recovery
Plan (see Part III) will protect occupied
habitat, protect other habitat that can
presumably be occupied in the near
future, and allow for “replacement”
habitat to develop and be sustained on
the landscape. Habitat monitoring as
required by this Recovery Plan should
provide data on habitat trends throughout
Recovery Plan duration.
2. The population will be monitored over
the life of the Recovery Plan, thus
providing insight as to whether the
current “baseline” population is sufficient
to maintain the subspecies over
time and testing the assumption that
the “baseline” population is adequate.
The Recovery Team did not make the
assumption that the “baseline” population
is adequate lightly, but reasoned
that the Mexican spotted owl is well
distributed throughout its historical
range, suggesting that no significant
extirpations have occurred.
Volume I/Part I
12
Mexican Spotted Owl Recovery Plan
Table able I.D.1. I.D.1. Summary of relative Mexican spotted owl population size, timber harvest threat, and
fire threat by U.S. Recovery Unit.
Thr Threat Thr eat S SSignificance
S ignificance
Reco eco eco ecover eco er ery er y U UUnit
U Unit
nit Population opulation Fir ir ir ire ir Timber imber
Colorado Plateau low moderate low
Southern Rocky Mtns-CO low high low
Southern Rocky Mtns-NM low high high
Upper Gila Mountains high high high
Basin and Range - West high high low
Basin and Range - East high high high
RECOVERY RECOVERY PLAN PLAN DURATION
DURATION
Any management plan must specify the time
period over which the plan is to be implemented.
The Recovery Team decided that a 10year
period is appropriate for the Mexican
Spotted Owl Recovery Plan (assuming the
delisting criteria specified in III.A are met) for
several reasons:
1. Ten years allows adequate time to monitor
the trends in population and habitat.
The charge of the Recovery Team was
to develop a plan that would lead to
recovery of the subspecies. In developing
the delisting criteria specified in III.A,
the Recovery Team reasoned that the
population must be stable or increasing
before the subspecies could be considered
for delisting. The Recovery Team
further determined that a monitoring
period of 10 years would provide information
about population trends that
could be used with a reasonably high
level of confidence. The five-year monitoring
period the Act requires after a
species is delisted will further increase
confidence in trend information.
2. A 10-year period should be sufficient
time to fill some of the major gaps in
existing knowledge, and accommodate
possible changes in future conditions.
Many aspects of Mexican spotted owl
biology remain unknown or poorly
understood. Consequently, the effects of

Volume I/Part I
different resource-management practices
on the fitness of individuals and on
population persistence remain unclear. A
better understanding of these relationships
is needed before a viable long-term
management plan can be developed.
Implementing the Recovery Plan includes
conducting the research activities
recommended in III.D; if these studies
are started immediately, 10 years should
be adequate to complete the majority of
them.
3. Uncertainty about the future could
render this Recovery Plan inadequate,
unacceptable, or otherwise obsolete.
Future events and developments could
have social, economic, environmental,
and other ramifications that cannot be
predicted. To try to plan beyond the next
decade or so would require an unjustified
confidence in our ability to predict the
state of our society and the environment.
4. Consistency with the requirements of the
Act. The Act requires that the status of
listed species be reviewed every five years.
This Recovery Plan constitutes an in–
depth status review of the Mexican
spotted owl, so a formal status review
should be conducted in years five and 10
of Recovery Plan implementation.
Unless new information or other developments
render this Recovery Plan
obsolete in the interim, the 10-year
point should mark the end of this
Recovery Plan and implementation of a
longer-term management strategy.
Several reviewers of the draft version of this
Recovery Plan pointed out that this relatively
short Recovery Plan duration fails to take into
account the long-term processes that have
influenced and will continue to influence
dynamic ecosystems. The Recovery Team believes,
however, that the management recommended
for the next few years was developed
with consideration of the long- and short-term
effects of these near-term management recommendations.
13
Mexican Spotted Owl Recovery Plan
Based on the foregoing points, the Recovery
Team recommends a Recovery Plan duration of
10 years unless data indicate that earlier revision
is appropriate, or that the applicable recommendations
be continued beyond that time. The
monitoring and research to be conducted during
the life of the Recovery Plan will resolve much
uncertainty surrounding the Mexican spotted
owl. The uncertainty about the future can never
be resolved, but a better understanding of
Mexican spotted owl natural history will enhance
our ability to create a long-term management
plan.
CONSERVATION CONSERVATION PLANS
PLANS
FOR FOR OTHER OTHER OTHER SPOTTED SPOTTED OWL
OWL
SUBSPECIES
SUBSPECIES
SUBSPECIES
Several conservation strategies have been
developed for the other spotted owl subspecies.
Perhaps the best known subspecies is the northern
spotted owl of the Pacific Northwest and
northwestern California. The northern subspecies
was listed as threatened in June 1990,
resulting in extensive conflict between conservation
of the subspecies and economic and social
interests of the Pacific Northwest, particularly
the timber industry.
The first management strategy was initiated
by the FS in the late 1970s. That approach,
which continued within some portions of the
subspecies’ range until 1990, was to manage
individual spotted owl territories, called Spotted
Owl Habitat Areas (SOHAs), or, earlier, Spotted
Owl Management Areas. Each SOHA consisted
of certain acreages that varied according to
location. Those territories were established
according to certain clustering and spacing
guidelines, and the general prescription for the
territories was to restrict timber harvest so that a
minimum “suitable habitat” acreage standard was
maintained in the territories. However, in certain
circumstances some harvest was allowed, such as
salvage harvest.
In 1989, in response to increasing controversy
over the spotted owl issue, the difficulty
the issue was causing land-management agencies,
and the proposed listing of the northern spotted
owl as a threatened species, the Interagency
Scientific Committee (ISC) was established. The

ISC produced “A Conservation Strategy for the
Northern Spotted Owl” (Thomas et al. 1990),
which recommended significant changes in
spotted owl management on public lands in the
Pacific Northwest. Briefly, the ISC delineated
large blocks of owl habitat, called Habitat
Conservation Areas (HCAs). The goal was to
delineate, where possible, HCAs known to
support or with the potential to support at least
20 spotted owl pairs. However, where 20-pair
HCAs were not possible, HCAs of 1 to 19 pairs
were delineated. The HCAs were spaced certain
distances from one another, depending on their
sizes. The HCAs were to be managed so that no
habitat degradation occurred within them,
protecting existing habitat and allowing previously
disturbed areas to return to a suitable
condition. The ISC envisioned eventual HCAs
where owl pairs could freely interact without
significant disruption of habitat continuity
between territories.
In addition, the ISC recommended managing
the areas between HCAs, termed the “forest
matrix,” according to the “50-11-40 rule.” This
rule prescribed that at least 50% of the forested
area within each quarter-township was to contain
trees averaging a minimum of 28 cm (11 in)
in diameter and with at least 40% crown closure.
The idea was that these conditions would allow
movement of owls between HCAs, thereby
allowing genetic flow and demographic rescue of
subpopulations. The ISC also recommended
retention of 28-ha (70-acre) areas within the
forest matrix to possibly provide future nesting/
roosting sites.
In 1991, the Secretary of the Interior appointed
the Northern Spotted Owl Recovery
Team and charged it with developing a recovery
plan for that subspecies. That recovery plan was
closely modeled after the ISC plan. The HCA
network was modified based on updated information,
resulting in a network of Designated
Conservation Areas (DCAs). Timber harvest in
DCAs was generally not allowed in suitable
habitat. Silvicultural treatments designed to
encourage spotted owl habitat were limited to no
more than 5% of a DCA in the first five years of
plan implementation. Management recommendations
for areas outside DCAs deviated from
the ISC approach by providing greater justifica-
Volume I/Part I
14
Mexican Spotted Owl Recovery Plan
tion for specific recommendations and consideration
of economic efficiency of implementation.
The Northern Spotted Owl Recovery Plan
was never implemented. Instead, the most recent
management strategy for the northern spotted
owl resulted from analyses and recommendations
formulated by the Forest Ecosystem Management
Assessment Team (FEMAT). The FEMAT
was appointed by President Clinton to develop
alternative plans for management of late-successional
ecosystem components including, but not
specific to, the northern spotted owl. Only
Federal land management was addressed in the
FEMAT alternatives.
The President selected “Option 9” developed
by the FEMAT, which calls for a series of Late
Successional Reserves (LSRs) corresponding
roughly to the HCAs under the ISC plan.
Outside the LSRs, the forest matrix includes
Riparian Reserves (various sized buffers along
class 1-3 streams); green-tree retention requirements
(where 15% of each watershed is managed
for late successional forest and at least 15% of
each harvest unit is retained in the latest successional
forest available); and preservation of 40 ha
(100 ac) around all owl sites known as of 1
January 1994. The goal of this matrix prescription
is to accommodate dispersing and “floater”
owls, as well as other species dependent on old
and mature forest conditions.
The FEMAT plan also establishes Adaptive
Management Areas (AMAs) in California,
Oregon, and Washington. These AMAs vary
from less than 40,500 ha (100,000 ac) to nearly
200,000 ha (500,000 ac). The management
objectives for each AMA also vary, but they are
generally established to develop and test techniques
for active forest management that provide
a wide range of resource values including forest
products, late-successional forest habitat, and
high-quality recreation.
The range of the California spotted owl
abuts the range of the northern subspecies in
northeastern California, ranging south through
the Sierra Nevada, west through the “transverse
ranges” of Southern California, then north along
the Coast Range to Monterey County. The
California spotted owl was first managed by the
FS using the SOHA system described for the
northern subspecies. The portion of the subspe-

cies’ range in Southern California is still managed
under that system while its effectiveness is
assessed. However, the current management
regime in the Sierra Nevada is described in the
“Assessment of the Current Status of the California
Spotted Owl, with Recommendations for
Management” (Caspow Plan) (Verner et al.
1992b). The FS implemented the Caspow Plan
on a temporary basis through an environmental
assessment under the National Environmental
Policy Act (NEPA) on 1 March 1993. The FS
has since released a draft environmental impact
statement under the NEPA that analyzes several
alternatives for California spotted owl management,
one of which is the Caspow Plan.
In the Sierra Nevada, the Caspow Plan
recommends management emphasizing adequate
amounts and distribution of suitable owl habitat
through improved habitat and resource management
practices rather than through protection of
large blocks of habitat. The strategy seeks to
protect known owl nest or roost sites, retain the
larger and older components of forest structure,
and address the problems of fire suppression and
fuel loading. Additional objectives include
rapidly recovering nesting and roosting habitat
following disturbance, maintaining existing
canopy layers, promoting tree growth by thinning
in middle and lower canopy layers, and
reducing vertical fuel ladders. Habitat available
for timber management is classified by structural
condition and utility for various life history
requirements, and the resultant habitat classes
are managed with restrictions on structural
modifications. Long-term management proposals
also focus on spotted owl nesting and roosting
habitat as the target conditions for silvicultural
activities.
To formulate the management strategy
contained in this Recovery Plan, the Recovery
Team examined the extensive efforts to protect
the California and northern spotted owl subspecies.
These efforts have, so far, experienced
varying degrees of success and controversy.
Moreover, the three subspecies exhibit differences
in habitat use, habitat distribution, and
threats. The Mexican Spotted Owl Recovery
Plan combines, in the Recovery Team’s opinion,
the applicable recommendations from other
Volume I/Part I
15
Mexican Spotted Owl Recovery Plan
planning efforts with those uniquely applicable
to the Mexican subspecies.
ECOSYSTEM ECOSYSTEM MANAGEMENT
MANAGEMENT
The development of ecosystem management
in the history of conservation plans for the
northern spotted owl was described by Meslow
(1993). Results of population and habitat
research were incorporated into landscape
designs involving reserves (HCAs) and interstitial
matrices, both of which are basic attributes
of landscape ecology (Diaz and Apostol 1993).
Further considerations of the ecosystem management
approach were extended to sympatric
Federal- and State-listed species. It was clear that
single-species management for the northern
spotted owl would have numerous impacts on
the many eligible but yet to be listed species
(USDI 1992; Block et al. 1995). Thomas et al.
(1993) described the relationship between the
ISC plan for the northern spotted owl and the
likelihood of viability for a suite of other species
closely associated with late-successional forest.
Verner et al. (1992) described numerous links
between the California spotted owl and associated
ecosystem components that it uses and
requires to survive. Assessments of other species,
such as northern goshawks (Reynolds et al.
1992) have also underscored the need to manage
large landscapes to provide adequate prey and
the diversity of habitats needed by those species.
Despite growing academic and professional
awareness of the need to manage entire ecosystems,
the Recovery Team is charged with development
of a recovery plan for a single species.
However, as the FWS and other land-management
agencies move toward managing entire
ecosystems, they are recognizing that singlespecies
management will never protect all of the
organisms that comprise the ecosystems upon
which target species depend. Furthermore, a
management plan for one species may conflict
with a management plan for a sympatric species
in absence of careful integration of the two
plans. Block and Brennan (1993) noted that the
management recommendations of the ISC for
the northern spotted owl were firmly based in
habitat management. In addition to habitat,
however, both ecosystem-oriented and popula-

tion-level considerations must be wed in conservation
planning (Gutiérrez 1994).
The recovery team considered the interaction
of populations, habitats, and ecosystems in
the development of this Recovery Plan. The
Recovery Team recognizes that numerous habitats
exist within the range of the Mexican spotted
owl and that not all of those habitats are
important to the subspecies. The Recovery Team
concentrated its management recommendations
on habitats known to be important to the owl
(see Parts II and III), while allowing other
ecosystem management objectives, such as
conservation of other species, to drive management
of habitats where spotted owls are a secondary
concern.
The Recovery Team believes that it is important
to evaluate the effects of implementing
Recovery Plan management recommendations
on other endangered, threatened, sensitive,
candidate, or other species of concern. In addition,
it is important that the recommendations
for Mexican spotted owl management be compared
with the recommendations in other
species’ recovery or management plans. If conflicts
are identified, they need to be resolved by
appropriate land managers and/or scientists.
An important objective in management of
forested ecosystems should be to address forest
health problems, return forested ecosystems to
conditions within their natural range of variation,
and work toward sustainable and resilient
ecosystems. The goals of this Recovery Plan and
ecosystem management principles are compatible.
Proper ecosystem management will provide
for landscapes in which spotted owls and other
ecosystem components persist within the range
of their evolutionary adaptations. The metric
used to measure progress should be the amount
of acreage successfully treated to meet a desired
result, and not commodity-based measures such
as “board feet” or “animal unit months.” Commodities
will undoubtedly be a byproduct of
forested ecosystem management, but should not
be the driving consideration.
ECONOMIC ECONOMIC CONSIDERATIONS
CONSIDERATIONS
Protecting threatened and endangered
species can conflict with other resource objec-
Volume I/Part I
16
Mexican Spotted Owl Recovery Plan
tives. These conflicts can become more intense
when species conservation efforts restrict economic
returns from lands people depend upon
for their livelihoods and communities depend
upon for their very existence. Whether conflicts
between species conservation and economic
return are real or perceived, human concerns
should be considered so long as the conservation
goal is achieved.
As mentioned previously, the Recovery
Team’s charge was to develop a plan that would
lead to recovery of the Mexican spotted owl.
However, specific cause-effect relationships of
many management activities on individual owls
and pairs or in relation to population processes
are not entirely clear. Given these uncertainties,
it may be tempting to take a conservative approach
to recovery by recommending cessation
of all anthropogenic activities for which effects
of the activity on the target species are poorly
understood. However, recommendations for
resource management should be based on
established information. The absence of needed
information should stimulate research, and the
results of that research should guide management.
The only way to understand the causeand-effect
relationships between management
actions and specific resources is by studying
them, preferably through controlled experiments.
The recommendations contained herein
allow most land-management activities to occur
provided that the effects of those activities are
evaluated during the recovery period. In addition,
the Recovery Plan recommends that
scientific monitoring of the Mexican spotted owl
population and its habitat should accompany
those activities to assess their impact on spotted
owl populations. If warranted, these activities
can be altered or eliminated if monitoring or
research indicates a significant risk to the spotted
owl population. In other cases, restrictions on
human activities are recommended where data
show a high likelihood that the spotted owl’s
persistence may be significantly compromised if
certain land-management practices continue.
Obviously, the decision on which activities
must be altered or eliminated and which may
proceed if closely monitored cannot be made
with absolute certainty. Such decisions require

professional judgement of the most qualified
scientists using the best available data. The FWS
selected the Recovery Team members with that
fact in mind. However, the FWS also intends to
use the expertise of others who may contribute
useful information to improve management of
the Mexican spotted owl.
Any conservation plan, regardless of species,
must include the considerations discussed above
when uncertainties exist. The FWS is confident
that this Recovery Plan, given its inherent
flexibility, has a high likelihood of leading to the
recovery of the Mexican spotted owl without
causing unacceptable levels of economic and
social hardship during its implementation.
HUMAN HUMAN INTERVENTION
INTERVENTION
AND AND NATURAL NATURAL NATURAL PROCESSES
PROCESSES
Much criticism directed at Mexican spotted
owl management centers on the concept that
today’s southwestern forests are in an unnatural
state; that grazing, fire suppression, forestry
practices, and other anthropogenic processes
have led to forest conditions much denser than
those existing during presettlement times. A
concurrent increase in mixed-conifer forests is
also believed to have occurred. These points
lead some to the conclusion that the Mexican
spotted owl population is at an all-time (and
unsustainable) high. The Recovery Team is
unaware of data that clearly support that conclusion,
and questions whether stands recently
converted to mixed-conifer forest possess the
structural characteristics utilized by the subspecies.
The Recovery Team acknowledges that
humans have had a pronounced influence on
contemporary forest conditions; however, the
effects of human activities on the Mexican
spotted owl population are unknown. Even if
one accepts that the spotted owl population in
mixed-conifer forest is unnaturally high, one
must also consider that other habitats that may
have been important historically, such as lowerand
middle-elevation riparian areas, have been
dramatically reduced. These two trends may be
offsetting, and the net gain or loss of spotted owl
carrying capacity can only be speculated upon.
Volume I/Part I
17
Mexican Spotted Owl Recovery Plan
It would be imprudent, if not impossible, to
develop a management plan for a species by
speculating on its status in the distant past;
rather, the appropriate approach is to acknowledge
that we are dealing with a drastically altered
landscape and that a return to presettlement
conditions is impossible. In that light, the
Recovery Team acknowledges that humans have
a major role to play in management of the
spotted owl and the forests of the Southwest.
The Recovery Team believes that a viable forestproducts
industry is critical in carrying out the
management actions recommended in this
Recovery Plan, making it an essential agent of
plan implementation.
DIFFERENCES DIFFERENCES BETWEEN
BETWEEN
THE THE DRAFT DRAFT AND AND FINAL FINAL
FINAL
RECOVERY RECOVERY RECOVERY PLANS
PLANS
The Recovery Team considered all comments
received on the draft Mexican Spotted
Owl Recovery Plan. In addition, the draft
Recovery Plan underwent extensive peer review
from both purposely selected reviewers and
“blind” reviewers selected by certain scientific
societies (see Appendix E). These reviews led to a
final Recovery Plan that differs substantially
from the draft version. We do not attempt to
detail every difference between the two versions
of the Recovery Plan, but discuss these differences
in general terms.
Part II of the draft Recovery Plan contained
a great deal of technical information. In the
interest of making the Recovery Plan an easier
document to use, several of those chapters were
placed in a companion volume to this Recovery
Plan. The information contained in those
chapters was integral to Recovery Plan development,
so the main points in each are summarized
in Part II of this final Recovery Plan.
Part III has changed substantially from the
draft version. Much of the background and
justification discussion has been moved to Part
II, so that the current Part III deals strictly with
the management recommendations and delisting
criteria. This allows land managers to more easily
pull the specific recommendations out of the
Part III text. In addition, the management

ecommendations have changed considerably, in
that they are now in a more descriptive, rather
than prescriptive, context. The changes were in
response to comments from numerous land
managers who expressed their concern that many
of the tools available to achieve land-management
objectives were overly constrained. The
Recovery Team recognizes that the best approach
is to describe the desired conditions on the
landscape, while providing land-management
professionals the flexibility to choose the tools to
achieve the stated objectives.
Volume I/Part I
18
Mexican Spotted Owl Recovery Plan
The most significant change in Part IV is
that the responsibility for implementing some of
the tasks recommended in this Recovery Plan
has been distributed among different entities. In
addition, the estimated costs of implementing
specific recovery tasks is provided.

Biological and Ecological Background
Volume I, Part II

Volume I/Part II
A. A. GENERAL GENERAL BIOLOGY
BIOLOGY
AND AND ECOLOGICAL ECOLOGICAL RELATIONSHIPS RELATIONSHIPS OF
OF
THE THE MEXICAN MEXICAN MEXICAN SPOTTED SPOTTED OWL
OWL
Sarah E. Rinkevich, Joseph L. Ganey, James P. Ward Jr.,
Gary C. White, Dean L. Urban, Alan B. Franklin,
William M. Block, and Fernando Clemente
This section presents a summary of
Volume 2, which examines aspects of the biology
and ecological relationships of Mexican spotted
owls in more detail. This is not an exhaustive
treatment of the owl’s biology and ecology, but is
intended to provide an overview of biological
elements germane to recovering the Mexican
spotted owl. Although gaps still exist, our
understanding of the Mexican spotted owl’s
natural history has increased with recent research
as well as data analyses accomplished by the
Recovery Team.
A wealth of information exists for the northern
and California spotted owls (Thomas et al.
1990, Bart et al. 1992, Verner et al. 1992a,
Gutiérrez et al., 1995). Although different in
some respects, many aspects of the owls’ biology
and ecology are similar among the three subspecies.
Thus, where appropriate, information from
these subspecies was used for comparison or
where data were limited regarding the Mexican
spotted owl.
TAXONOMY
TAXONOMY
Three species within the genus Strix occur
north of Mexico: spotted (S. occidentalis), barred
(S. varia), and great gray owls (S. nebulosa).
Mexican spotted, barred, and fulvous owls (S.
fulvescens) occur in Mexico. The Mexican spotted
owl (S. o. lucida) is one of three subspecies of
spotted owl recognized by the American Ornithologists’
Union (AOU) in its last checklist that
included subspecies (AOU 1957:285). The other
two subspecies are the northern (S. o. caurina)
and the California spotted owl (S. o. occidentalis)
(AOU 1957; Figure.II.A.1).
The Mexican subspecies was first described
from a specimen collected at Mount Tancitaro,
Michoacan, Mexico and named Syrnium
occidentale lucidum (Nelson 1903). The spotted
owl was later assigned to the genus Strix
19
Mexican Spotted Owl Recovery Plan
(Ridgway 1914) and the subspecific name was
changed to lucida to conform to taxonomic
standards. Monson and Phillips (1981) regarded
the Mexican spotted owl in Arizona as S. o.
huachucae, noting that they were paler than S. o.
lucida. However, this taxonomic designation was
not followed by the AOU (1957).
The Mexican subspecies is geographically
isolated from both the California and northern
subspecies. Using electrophoresis to examine
allozyme variation, Barrowclough and Gutiérrez
(1990) found a major allelic difference between
the Mexican spotted owl and the two coastal
subspecies. This difference suggests that the
Mexican spotted owl has been isolated genetically
from the other subspecies for considerable
time, has followed a separate evolutionary
history, and could therefore be considered a
separate species (Barrowclough and Gutiérrez
1990:742).
Northern spotted owls are known to hybridize
with barred owls. Hybrids have been found
in Washington and Oregon (Hamer et al. 1992),
and in California (Alan Franklin, Humboldt
State Univ., Arcata, CA, pers. comm.). The
hybrids can be identified by their plumage,
vocalizations, and morphology (Hamer et al.
1992). Closely related species occasionally
hybridize naturally, especially where habitat
disruption has led to contact between species
previously isolated geographically (Short 1965,
1972). Hybridization has not been reported in
the Mexican subspecies. The possibility of
hybridization exists in Mexico where barred
owls, fulvous owls, and spotted owls overlap in
distribution. No evidence currently exists documenting
actual sympatry among these species,
however.

Figur igur igure igur e II.A.1. II.A.1. Geographic range of the spotted owl.
Volume I/Part II
20
Mexican Spotted Owl Recovery Plan

Volume I/Part II
DESCRIPTION
DESCRIPTION
The spotted owl is mottled in appearance
with irregular white and brown spots on its
abdomen, back, and head. The spots of the
Mexican spotted owl are larger and more numerous
than in the other two subspecies, giving it a
lighter appearance. Strix occidentalis translates as
“owl of the west” and lucida means “light” or
“bright.” Unlike most owls, spotted owls have
dark eyes. Several thin white bands mark an
otherwise brown tail.
Adult male and female spotted owls are
mostly monochromatic in plumage characteristics,
but the sexes can be readily distinguished by
voice (see below). Juveniles, subadults, and
adults can be distinguished by plumage characteristics
(Forsman 1981, Moen et al. 1991).
Juvenile spotted owls (hatchling to approximately
five months) have a downy appearance.
Subadults (5 to 26 months) closely resemble
adults, but have pointed retrices with a pure
white terminal band (Forsman 1981, Moen et al.
1991). The retrices of adults (>27 months) have
rounded tips, and the terminal band is mottled
brown and white.
Although the spotted owl is often referred to
as a medium-sized owl, it ranks among the
largest owls in North America. Of the 19 species
of owls that occur in North America, only 4 are
larger than the spotted owl (Johnsgard 1988).
Like many other owls, spotted owls exhibit
reversed sexual dimorphism (i.e., females are
larger than males). Adult male Mexican spotted
owls (n = 37) average 519 + 32.6 (SD) g
(18.5 oz), and adult females (n = 31) average 579
+ 31.2 g (20.7 oz) (Kristan et al., in prep.).
There appears to be clinal variation among the
three subspecies in a number of morphological
characteristics measured, with size decreasing
from north to south (Kristan et al., in prep.).
DISTRIBUTION
DISTRIBUTION
AND AND ABUNDANCE
ABUNDANCE
The Recovery Team gathered and examined
information on the distribution and abundance
of Mexican spotted owls through 1993. Data
from surveys conducted after 1993 were not
available for our analyses.
21
Mexican Spotted Owl Recovery Plan
We used the information collected to (1)
document historical and current range of this
subspecies, (2) help formulate Recovery Unit
boundaries, and (3) provide a template for
analyses at the landscape scale. Descriptions of
Recovery Units are provided in the following
chapter (II.B).
The Mexican spotted owl currently occupies
a broad geographic area, but does not occur
uniformly throughout its range (Figure II.A.2).
Instead, the owl occurs in disjunct localities that
correspond to isolated mountain systems and
canyons. In the United States, 91% of the owls
known to exist between 1990 and 1993 occur on
lands administered by the FS (Table II.A.1).
Other lands currently occupied by Mexican
spotted owls in the United States include, NPS
(4%), BLM (2%), Tribal (2%), and DOD (1%).
We know that more owls occur on Tribal lands
than indicated here, but specific information on
numbers of owls known on Tribal lands was not
made available to the Team. Owl distribution
according to land ownership is unavailable for
Mexico. Eighty-nine percent of the owls known
to exist between 1990 and 1993 in Mexico were
in the States of Sonora and Chihuahua (Table
II.A.1, Figure II.A.3). However, most survey
efforts in Mexico were restricted to these states,
and these numbers do not necessarily reflect
actual trends in distribution.
The current owl distribution mimics its
historical extent, with a few exceptions. The owl
has not been reported recently along major
riparian corridors in Arizona and New Mexico,
nor in historically documented areas of southern
Mexico. Riparian communities and previously
occupied localities in the southwestern United
States and southern Mexico have undergone
significant habitat alteration since the historical
sightings (USDI 1993). However, the amount of
effort devoted to surveying these areas is unknown
and future surveys may document
spotted owls there. Surveys conducted to relocate
spotted owls in northern Colorado near Fort
Collins and Boulder, where records exist from
the early 1970s and 1980s, have been unsuccessful.
Surveys conducted in the Book Cliffs of eastcentral
Utah, where owls were recorded in 1958,
have also been unsuccessful. Although historical
(pre-1990) data provide some information about

Volume I/Part II
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e II.A.2. II.A.2. Current distribution of Mexican spotted owls in the United States based on planned
surveys and incidental observations recorded from 1990 through 1993.
22

Volume I/Part II
Mexican Spotted Owl Recovery Plan
Table able II.A.1. II.A.1. Historical records and minimum numbers of Mexican spotted owls found during
planned surveys and incidental observations, reported by Recovery Unit and land ownership. Recovery
Units are described in Part II.B.
Number umber of of 1 N NNumber
N umber of
of
owl wl r rrecor
rr
ecor ecords ecor ds o oowl
o wl sites
sites
Reco eco eco ecover eco er er ery er y U UUnit
U nit befor before befor e 1990 1990
1990-1993
1990-1993
UNITED UNITED ST STATES ST TES
Colorado Plateau
FS 21 16
BLM 6 10
NPS 34 23
Tribal 20 13 2
New Mexico State 1 0
Unknown 3 5 0
Subtotal ubtotal Southern Rocky Mountains – Colorado
87 87
62
62
FS 2 8
BLM 0 6
NPS 0 0
Tribal 1 -- 2
Unknown 3 17 0
Subtotal ubtotal Southern Rocky Mountains – New Mexico
20 20 20
14
14
FS 25 34
NPS 3 0
New Mexico State 1 0
Private 4 0
Unknown 3 8 0
Subtotal ubtotal Upper Gila Mountains
41 41
34
34
FS 138 424
BLM 5 0
NPS 5 0
Tribal 0 -- 2
Private 1 0
Unknown 3 104 0
Subtotal ubtotal Basin and Range – West
253 253
424
424
FS 82 97
NPS 13 0
Tribal 0 -- 2
DOD 9 6
Private 8 0
Unknown 3 57 0
Subtotal ubtotal 169 169
103
103
23

Table able II.A.1. II.A.1. continued
Number umber of of 1 Number umber of
of
owl wl r rrecor
rr
ecor ecords ecor ds owl wl sites
sites
Reco eco eco ecover eco er ery er y U UUnit
U Unit
nit befor before befor e 1990 1990 1990
1990-1993 1990-1993
1990-1993
Basin and Range – East
FS 18 111
BLM 1 0
NPS 6 10
Tribal 2 -- 2
FWS 1 0
Private 2 0
Subtotal ubtotal 30 30
121
121
United nited nited SS
States S States
tates Total otal 600 600
758
758
MEXICO
MEXICO
Sierra Madre Occidental – Norte
Sonora 8 9
Chihuahua 10 8 4
Subtotal ubtotal Sierra Madre Oriental – Norte
18 18
17
17
Coahuila
Sierra Madre Occidental – Sur
2 0
Sinaloa 1 0
Durango 2 0
Aguacalientes 0 1 4
Zacatecas 0 0 4
San Luis Potosi 1 0
Guanajuato 1 0
Subtotal ubtotal Sierra Madre Oriental – Sur
5 5
1
1
Coahuila 4 0
Nuevo Leon 4 1
Tamaulipas 0 0 4
Subtotal ubtotal Eje Neovolcanico
8 8
1
1
Jalisco 1 0
Colima 1 5 0
Michoacan 1 0
Puebla 1 5 0
Subtotal ubtotal 2 2
0
0
Mexico exico exico Total otal 35 35 35
19
19
Volume I/Part II
Mexican Spotted Owl Recovery Plan
1
These values do not necessarily indicate numbers of owls or owl sites because multiple records may exist from the
same site through time.
2 Additional owls are known to exist on many Tribal lands, but the exact number is unavailable.
3
Locations of these records were insufficient for assigning a land ownership.
4 Additional sightings have been reported from 1994 surveys.
5 Unverified record not included in totals (see text).
24

Volume I/Part II
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e II.A.3. II.A.3. Current distribution of Mexican spotted owls in Mexico based on planned surveys
and incidental observations recorded from 1990 through 1993.
25

about past distribution of spotted owls, we stress
that it is not sufficient to allow us to estimate
changes in the number or distribution of owls
from historical to present time.
Most current observations of Mexican
spotted owls are from the Upper Gila Mountains
RU (see II.B). This unit can be considered a
critical nucleus for the subspecies because of its
central location within the owl’s range and its
seemingly high number of owls. Other areas
likely to be important population centers include
the sky islands of southeastern Arizona and
the Sacramento Mountains of central New
Mexico (Basin and Range RUs; see II.B). Although
information on owl numbers permits a
view of the current distribution, it is not complete
enough to provide a reliable estimate of
total population size.
Mexican spotted owls occur at higher densities
in mixed-conifer forests than in pine-oak,
pine, and pinyon-juniper forest types (Skaggs
and Raitt 1988, White et al. 1995). A combined
estimate of Mexican spotted owl density on two
study areas in the Upper Gila Mountains RU is
similar to estimates reported for other spotted
owl subspecies.
In summary, the Mexican spotted owl is
distributed discontinuously throughout its
range, with its distribution largely restricted to
montane forests and canyons. Although future
efforts will undoubtedly discover additional
owls, their documented spatial distribution in
the United States is not likely to change greatly.
The converse is true for Mexico, where planned
surveys have begun only recently.
HABITAT HABITAT HABITAT ASSOCIATIONS
ASSOCIATIONS
Mexican spotted owls nest, roost, forage, and
disperse in a diverse array of biotic communities.
Mixed-conifer forests are commonly used
throughout most of the range (Johnson and
Johnson 1985, Skaggs and Raitt 1988, Ganey et
al. 1988, Ganey and Balda 1989a, Rinkevich
1991, Willey 1993, Fletcher and Hollis 1994,
Seamans and Gutiérrez, in press). In general,
these forests are dominated by Douglas-fir and/
or white fir, with codominant species including
southwestern white pine, limber pine, and
ponderosa pine (Brown et al. 1980). The under-
Volume I/Part II
26
Mexican Spotted Owl Recovery Plan
story often contains the above coniferous species
as well as broadleaved species such as Gambel
oak, maples, boxelder, and New Mexico locust.
In southern Arizona and Mexico, Madrean pineoak
forests are also used commonly (Ganey and
Balda 1989a, Duncan and Taiz 1992, Ganey et
al. 1992, Tarango et al. 1994). These forests are
typically dominated by an overstory of Chihuahua
and Apache pines in conjunction with
species such as Douglas-fir, ponderosa pine, and
Arizona cypress. Evergreen oaks are typically
prominent in the understory (Brown et al.
1980).
Habitat-use patterns vary throughout the
range and with respect to owl activity (see
below). In the northern portion of the range,
including southern Utah, southern Colorado,
and far northern Arizona and New Mexico, owls
occur primarily in steep-walled, rocky canyons
(Kertell 1977, Reynolds 1990, Rinkevich 1991,
Willey 1993). Along the Mogollon Rim in
Arizona and New Mexico, habitat use is less
restricted, and spotted owls occur in mixedconifer
forests, ponderosa pine-Gambel oak
forests, rocky canyons, and associated riparian
forests (Ganey and Balda 1989a, Ganey et al.
1992, Fletcher and Hollis 1994, Seamans and
Gutiérrez, in press, Peter Stacey, Univ. of
Nevada, Reno, pers. comm.). South of the
Mogollon Rim and into Mexico a still wider
variety of habitat types are used, including
mixed-conifer, Madrean pine-oak, and Arizona
cypress forests, encinal oak woodlands, and
associated riparian forests (Ganey and Balda
1989a, Duncan and Taiz 1992, Ganey et al.
1992, Tarango et al. 1994). Much of this regional
variation in habitat use likely results from
differences in regional patterns of habitat and
prey availability.
Nesting Nesting and and Roosting Roosting Habitat
Habitat
Mexican spotted owls nest and roost primarily
in closed-canopy forests or rocky canyons. In
the northern portion of the range (southern
Utah and Colorado), most nests are in caves or
on cliff ledges in steep-walled canyons. Elsewhere,
the majority of nests appear to be in trees
(Fletcher and Hollis 1994).

Forests used for roosting and nesting often
contain mature or old-growth stands with
complex structure (Skaggs and Raitt 1988,
Ganey and Balda 1989a, 1994; McDonald et al.
1991, Seamans and Gutiérrez, in press). These
forests are typically uneven-aged, multistoried,
and have high canopy closure. Nest trees are
typically large in size (SWCA 1992, Fletcher and
Hollis 1994, Seamans and Gutiérrez, in press),
whereas owls roost in both large and small trees
(Ganey 1988, Rinkevich 1991, Willey 1993,
Zwank et al. 1994, Peter Stacey, Univ. of
Nevada, Reno, pers. comm.). Tree species used
for nesting vary somewhat among areas and
habitat types, but available evidence suggests that
Douglas-fir is the most common species of nest
tree (SWCA 1992, Fletcher and Hollis 1994,
Seamans and Gutiérrez, in press). A wider variety
of trees are used for roosting, but again Douglasfir
is the most commonly used species (Ganey
1988, Fletcher and Hollis 1994, Zwank et al.
1994, Peter Stacey, Univ. of Nevada, Reno, pers.
comm.).
Several hypotheses have been proposed to
explain why spotted owls nest in closed-canopy
forests (reviewed by Carey 1985, Gutiérrez
1985). Barrows (1981) suggested that spotted
owls are relatively intolerant of high temperatures
and roost and nest in shady forests because
they provide favorable microclimatic conditions.
Ganey et al. (1993) observed that Mexican
spotted owls produced more metabolic heat than
great horned owls, and were less able to dissipate
that heat. This may lead these owls to seek out
cool microsites during periods of high ambient
temperature. Mexican spotted owls typically nest
and roost in closed-canopy forests or deep shady
canyons; both situations provide cool microsites
(Kertell 1977, Ganey et al. 1988, Rinkevich
1991, Ganey and Balda 1989a, Willey 1993).
Foraging Foraging Habitat
Habitat
Little is known about patterns of habitat use
by foraging owls. The only available data describe
habitat use by eight owls occupying five
home ranges on three study areas in northern
Arizona (Ganey and Balda 1994). In general,
owls foraged more than or as expected in
unlogged forests, and less than or as expected in
Volume I/Part II
27
Mexican Spotted Owl Recovery Plan
selectively logged forests. Expected values were
based on relative occurrences of habitats. However,
patterns of habitat use varied among study
areas and individuals, and even between pair
members in some cases, making generalizations
difficult. Both high-use roosting and high-use
foraging sites had more big logs, higher canopy
closure, and greater densities and basal areas of
both trees and snags than random sites. Owls
clearly used a wider variety of forest conditions
for foraging than they used for roosting (Ganey
and Balda 1994). We caution, however, about
extending these results too far given the limited
number of owls sampled, and the variability
observed among owls and sites.
TERRITORIALITY
TERRITORIALITY
AND AND HOME HOME HOME RANGE RANGE
RANGE
Home range is defined as the area used by an
animal during its normal activities (Burt 1943)
whereas territory is a defended area within an
individual’s home range (Nice 1941). Territories
are typically smaller than home ranges, but the
exact relationship between the territory and the
home range is generally not known. Fidelity to
territories is apparently high in Mexican spotted
owls, with most owls remaining on the same
territory year after year.
Home-range size of Mexican spotted owls,
as estimated by monitoring movements of
radiotagged owls, appears to vary considerably
among habitats and/or geographic areas (Ganey
and Dick 1995). Differences in sampling methods
among studies make comparisons difficult,
however. Minimum convex polygon home
range estimates of home range-size varied
from (1) 924 - 1,487 ha (2,282 - 3,672 acres)
for individuals (n = 11) on three study areas in
Colorado Plateau RU (Willey 1993); (2) 261 -
1,053 ha (645 - 2,601 acres) for individuals
(n = 25) and 381 - 1,551 ha (941 - 3,831 acres)
for pairs (n = 10) on five study areas in the
Upper Gila Mountains RU (Ganey and Balda
1989b, Ganey and Block, unpublished data,
Peter Stacey, Univ. of Nevada, Reno, pers.
comm.); and (3) 452 - 937 ha (1,116 - 2,314
acres) for individuals (n = 20) and 573 - 1,401
ha (1,415 - 3,461 acres) for pairs (n = 8) on two
study areas in the Basin and Range-East RU

(Zwank et al. 1994, Ganey and Block, unpublished
data).
Volume I/Part II
VOCALIZATIONS
VOCALIZATIONS
The spotted owl, being primarily nocturnal,
is more often heard than seen. It has a wide
repertoire of calls (Forsman et al. 1984, Ganey
1990) that are relatively low-pitched and composed
of pure tones (Fitton 1991). Sexes can be
distinguished by calls; males have a deeper voice
than females and generally call more frequently.
The most common vocalization, used more
often by males, is a series of four unevenlyspaced
hoots. Females frequently use a clear
whistle ending with an upward inflection as well
as a series of sharp barks. Forsman et al. (1984)
described 14 calls for the northern spotted owl,
of which 10 were reported by Ganey (1990) for
Arizona birds.
Mexican spotted owls call mainly from
March - November and are relatively silent from
December - February (Ganey 1990). Calling
activity increases from March through May
(although nesting females are largely silent
during April and early May), and then declines
from June through November (Ganey 1990).
On a daily basis, calling activity is greatest
during the 2-hour period following sunset, with
smaller peaks 4-8 hours after sunset and just
before sunrise. Owls called more than expected
during the last quarter and new moon phases of
the lunar cycle; and they called most frequently
on calm, clear nights when no precipitation was
falling (Ganey 1990).
INTERSPECIFIC INTERSPECIFIC COMPETITION
COMPETITION
Several other species of owls occur within the
range of the Mexican spotted owl. Interference
competition, where individuals physically
interfere with each other, probably does not
occur to any great extent between the Mexican
spotted owl and other owl species. However,
exploitative competition, where individuals
compete for similar resources such as prey or
nest sites, may occur. Competition might be
greatest between spotted and great horned owls
because both species are relatively large and
widely distributed. Preliminary data from a
Mexican Spotted Owl Recovery Plan
telemetry study in northern Arizona suggest that
these owls overlap broadly in diet and space, but
exhibit some habitat segregation (Ganey and
Block, unpublished data). If Mexican spotted
and barred owls are sympatric in Mexico, then
competition might also occur between these
closely related species. In general, however, more
research is needed to assess the potential occurrence
and importance of interspecific competition
between spotted and other owls.
FEEDING FEEDING HABITS HABITS AND AND PREY
PREY
ECOLOGY
ECOLOGY
Forsman (1976) described spotted owls as
“perch and pounce” predators. They typically
locate prey from an elevated perch by sight or
sound, then pounce on the prey and capture it
with their talons. Spotted owls have also been
observed capturing flying prey such as birds and
insects (Verner et al. 1992b). They hunt primarily
at night (Forsman et al. 1984, Ganey 1988),
although infrequent diurnal foraging has been
documented (Forsman et al. 1984, Laymon
1991, Sovern et al. 1994).
Mexican spotted owls consume a variety of
prey throughout their range but commonly eat
small- and medium-sized rodents such as
woodrats, peromyscid mice, and microtine voles.
Spotted owls also consume bats, birds, reptiles,
and arthropods. The diet varies by geographic
location (Ward and Block 1995; Figure. II.A.4).
For example, spotted owls dwelling in canyons
of the Colorado Plateau take more woodrats,
and fewer birds, than do spotted owls from other
areas (Ward and Block 1995, Figure. II.A.4). In
contrast, spotted owls occupying mountain
ranges with forest-meadow interfaces, as found
within the Basin and Range - East, Southern
Rocky Mountains - Colorado, and Upper Gila
Mountains RUs, take more voles (Ward and
Block 1995, Figure. II.A.4). Regional differences
in the owl’s diet likely reflect geographic variation
in population densities and habitats of both
the prey and the owl.
The Team was unable to link consumption
of specific prey and successful reproduction by
the Mexican spotted owl, with two possible
exceptions. First, fecundity of spotted owls
occupying the Sacramento Mountains (Basin
28

and Range - East RU) appeared to be associated
with trends in abundance of peromyscid mice
(Ward and Block 1995). Second, the predominance
of woodrats in the diet throughout much
of the owl’s range suggests that this prey may
influence the owl’s fitness. Other studies have
shown positive associations between larger prey
(e.g., woodrats) in the diet of northern and
California spotted owls and their reproductive
success (Barrows 1987, Thrailkill and Bias
1989). In most cases, however, total prey biomass
may be more influential on the owl’s fitness
than the abundance of any particular prey
species.
Habitat correlates of the owl’s common prey
emphasize that each prey species uses a unique
microhabitat. For example, deer mice are ubiquitous
in distribution, occupying areas with
variable conditions, whereas brush mice are
restricted to communities with a strong oak
component and dry, rocky substrates with sparse
tree cover. Mexican woodrats are typically found
in areas with considerable shrub or understory
tree cover, little herbaceous cover, and high log
volumes. Mexican voles are found in areas with
high herbaceous cover, primarily grasses. Longtailed
voles are associated with high herbaceous
cover, primarily forbs, many shrubs, and limited
tree cover. Thus, to provide a diverse prey base,
managers should provide diverse habitats for
prey species. Managing habitat for a diversity of
prey species may help buffer against population
fluctuations of individual prey species and
provide a more constant food supply for the owl.
REPRODUCTIVE REPRODUCTIVE BIOLOGY
BIOLOGY
Knowledge of the annual reproductive cycle
of the Mexican spotted owl is important both in
an ecological context, and for placing seasonal
restrictions on management or on other activities
that may occur within areas occupied by spotted
owls. Data on the reproductive cycle of the
Mexican spotted owl are limited compared to
information on the northern and California
subspecies. Therefore, although the following
discussion is based primarily on observations of
the Mexican spotted owl, data from the other
subspecies are provided to fill some information
gaps.
Volume I/Part II
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Mexican Spotted Owl Recovery Plan
Mexican spotted owls nest on cliff ledges,
stick nests built by other birds, debris platforms
in trees, and in tree cavities (Johnson and
Johnson 1985, Ganey 1988, SWCA 1992,
Fletcher and Hollis 1994, Seamans and
Gutiérrez, in press). Spotted owls have one of
the lowest clutch sizes among North American
owls (Johnsgard 1988). Females normally lay
one to three eggs, two being most common. Renesting
following nest failure is unusual, but has
been observed in Mexican spotted owls (Kroel
1991, David Olson, Humboldt State Univ.,
Arcata, CA, pers. comm.). Mexican spotted owls
breed sporadically and do not nest every year
(Ganey 1988). In good years most of the population
will nest, whereas in other years only a
small proportion of pairs will nest successfully
(Fletcher and Hollis 1994). Reasons for this
pattern are unknown.
Mexican spotted owls have distinct
annual breeding periods, but reproductive
chronology varies somewhat across the range of
the owl. In Arizona, courtship apparently begins
in March with pairs roosting together during the
day and calling to each other at dusk (Ganey
1988). Eggs are laid in late March or, more
typically, early April. Incubation begins shortly
after the first egg is laid, and is performed
entirely by the female (Ganey 1988). Female
northern spotted owls incubate for approximately
30 days (Forsman et al. 1984), and
Mexican spotted owls appear to incubate for a
similar period (Ganey 1988). During incubation
and the first half of the brooding period, the
female leaves the nest only to defecate, regurgitate
pellets, or to receive prey delivered by the
male, who does most or all of the foraging
(Forsman et al. 1984, Ganey 1988).
The eggs usually hatch in early May (Ganey
1988). Females brood their young almost
constantly for the first couple of weeks after the
eggs hatch but then begin to spend time hunting
at night, leaving the owlets unattended for up to
several hours (Eric Forsman, FS, Corvallis, OR,
pers. comm.). Nestling owls generally fledge four
to five weeks after hatching in early to mid-June
(Ganey 1988). Owlets usually leave the nest
before they can fly, jumping from the nest on to
surrounding tree branches or the ground
(Forsman et al. 1984, Ganey 1988). Owlets that

Volume I/Part II
Mexican Spotted Owl Recovery Plan
Figur igur igure igure
e II.A.4. II.A.4. Geographic variability in the food habits of Mexican spotted owls presented as relative
frequencies of (a) (a) (a) woodrats, (b) (b) voles, (c) (c) gophers, (d) (d) birds, (e) (e) bats, and (f (f (f) (f (f reptiles. Point values are
from single studies or averages among the number of studies shown in parenthesis (a) (a) (a). (a) (a) Vertical bars are
95% confidence intervals showing sampling and interstudy variation within a recovery unit. Recovery
unit acronyms are COPLAT-Colorado Plateau; SRM-CO-Southern Rocky Mountain-Colorado; SRM-
NM-Southern Rocky Mountain-New Mexico; UPGIL-Upper Gila Mountain; BAR-W-Basin and
Range - West; BAR-E-Basin and Range - East; SMO-N-Sierra Madre Occidental-Norte.
30

end up on the ground will often climb back up a
tree to a safe roost site. The mobility and foraging
skills of owlets improve gradually during the
summer. Within a week after leaving the nest,
most owlets can make short, clumsy flights
between trees. Three weeks after leaving the nest,
owlets can hold and tear up prey on their own
(Forsman et al. 1984).
Fledglings depend on their parents for food
during the early portion of the fledgling period.
Hungry owlets give a persistent, raspy “begging
call,” especially when adults appear with food or
call nearby (Forsman et al. 1984, Ganey 1988).
Begging behavior declines in late August, but
may continue at low levels until dispersal occurs,
usually from mid September to early October
(Ganey and Block, unpubl. data, Peter Stacey,
Univ. of Nevada, Reno, pers. comm., David
Willey, Northern Arizona Univ., Flagstaff, pers.
comm.).
Volume I/Part II
MORTALITY MORTALITY MORTALITY FACTORS
FACTORS
Several mortality factors (discussed below)
have been identified as potentially important
with respect to the Mexican spotted owl. Although
a number of owls have been recovered
following mortality and examined by both field
biologists and laboratory personnel, in general
little is known about the extent or importance of
these mortality factors.
Predation
Predation
Predation, particularly by avian predators,
may be a common mortality factor of spotted
owls. Potential avian predators of Mexican
spotted owls include great horned owls, northern
goshawks, red-tailed hawks, and golden eagles.
Some of these predators occupy the same general
habitats as the spotted owl, but there is little
direct evidence that they prey on spotted owls to
any great extent (Gutiérrez et al. 1995). Ganey
(1988) reported one instance of apparent great
horned owl predation on an adult spotted owl,
and Richard Reynolds (FS, Fort Collins, CO.,
pers. comm.) reported a golden eagle preying on
a spotted owl. Preliminary results from radiotagged
Mexican spotted owls indicate that both
31
Mexican Spotted Owl Recovery Plan
adults and juveniles are preyed upon (Willey
1993, Ganey and Block, unpubl. data), but in
most cases the identity of the predator was
unknown. Further, in southern Arizona,
procyonid mammals were observed attempting
to raid cliff site nests occupied by spotted owls
(Russell Duncan, Southwestern Field Biologists,
Tucson, AZ, pers. comm.). Thus, the extent to
which Mexican spotted owls are preyed upon is
unknown at this time.
Starvation
Starvation
Starvation is likely another common source
of mortality. Juvenile northern spotted owls may
be more vulnerable to starvation than adults
(Gutiérrez et al. 1985, Miller 1989), because of
their poor hunting skills. Starvation may also
result from low abundance or availability of prey,
which could affect both adults and juveniles.
Both adult and juvenile owls radio-tagged in
Arizona have been found dead of apparent
starvation (Ganey and Block, unpublished data),
and two of seven radio-tagged juveniles in Utah
died of starvation (Willey 1993). Most instances
of starvation occurred from late fall through
winter, when prey resources were reduced in
abundance and availability (Willey 1993, Block
and Ganey, unpublished data). In addition,
starvation may predispose young or even adults
to predation.
Accidents
Accidents
Accidents may be another mortality factor.
For example, instances of spotted owls being hit
by cars have been documented (Roger Skaggs,
New Mexico State Univ, Las Cruces, pers.
comm; Russell Duncan, Southwestern Field
Biologists, Tucson, AZ, pers. comm.). Owls
flying at night might also collide with
powerlines, tree branches, or other obstacles.
This might be particularly true for birds migrating
or dispersing through unfamilar terrain.
Again, little information is available on how
frequently this might occur.

Disease Disease and and Parasites
Parasites
Little is known about how disease and
parasites contribute to mortality of spotted owls.
Hunter et al. (1994) found a larval mite and lice
on 2 of 28 museum specimens of Mexican
spotted owls examined for parasites, and 6 of 18
live owls examined had hippoboscid fly larvae in
their ears. Some of the live owls examined also
had lice. Hunter et al. (1994) reached no conclusions
concerning mortality and ectoparasites in
spotted owls, but did suggest that larval infestations
in their ears could affect the owls’ hearing.
Because hearing is important for foraging at
night, such infestations could impact the birds’
ability to hunt effectively.
In general, however, spotted owls may be
adapted to high parasite loads. In a survey of
blood parasites in all three subspecies of spotted
owls, Gutiérrez (1989) found an infection rate of
100 percent. Although disease and parasites
could predispose owls to death by starvation,
predation, or accident, no evidence exists documenting
disease and parasites as direct mortality
factors within the Mexican subspecies.
Volume I/Part II
POPULATION POPULATION BIOLOGY BIOLOGY
BIOLOGY
The Mexican Spotted Owl population for a
specific area can be modeled with the simple
equation
N t+1 = N t + B t - D t + I t - E t ,
where N t is the population size at time t, B t is the
number of new birds recruited into the population
(births), D t is the number of birds dying, I t
is the number of birds immigrating into the
population, and E t is the number of birds emigrating
from the population. The combined
effect of births, deaths, immigrations, and
emigrations dictate the viability of the population,
and hence its long-term persistence.
Survival
Survival
Annual survival rates of adult Mexican
spotted owls is 0.8-0.9 based on short-term
population and radio-tracking studies and
longer-term monitoring studies (White et al.
32
Mexican Spotted Owl Recovery Plan
1995). These annual survival estimates can be
viewed as the probability of an individual surviving
from one year to the next or as the proportion
of individuals that will survive from one
year to the next. A variety of different estimators
of adult survival using different types and sets of
data gave similar results.
Juvenile survival is considerably lower ( 0.06-
0.29) than adult survival. Juvenile survival also
appears more spatially variable, although this
conclusion reflects only two population study
areas and two radio-telemetry studies spanning
two years or less.
We strongly suspect that estimates of juvenile
survival from the population studies which
utilize mark-recapture methods are biased low
because of (1) a high likelihood of permanent
dispersal (emigration) from the study area, and
(2) a lag of several years before marked juveniles
reappear as territory holders, at which point they
are first detected for recapture. Juvenile northern
spotted owls have a high dispersal capability
(reviewed in Thomas et al. 1990). If Mexican
spotted owl juveniles have a similar dispersal
capability, we expect that a substantial portion of
marked juveniles will emigrate from the respective
study areas. However, estimates from the
radio-telemetry studies roughly corroborated the
low estimates from the population studies. Biases
in the radio-telemetry estimates of juvenile
survival can result if radios significantly affect
their survival. Whether radios or their attachment
affect survival of northern spotted owls is
debatable (Paton et al. 1991, Foster et al. 1992).
Concerning the second point, Franklin (1992)
found a lag of 1-4 years between the time when
juvenile northern spotted owls were banded and
subsequently recaptured. If this process is similar
for Mexican spotted owls, then the current
population studies may be of insufficient duration
to adequately estimate juvenile survival.
In summary, current survival estimates are
based primarily on studies of insufficient duration
or studies not explicitly designed to estimate
survival. In most cases, the data are too limited
to support or test the assumptions of the estimators
used. However, the age- and sex-specific
estimates of survival calculated here are useful at
this point as qualitative descriptors of the lifehistory
characteristics of Mexican spotted owls.

That is, Mexican spotted owls exhibit high adult
and relatively low juvenile survival. In this
respect, Mexican spotted owl survival probabilities
appear similar to northern (see review in
Burnham et al. 1994) and California spotted
owls (Noon et al. 1992).
Reproduction
Reproduction
Reproductive output of Mexican spotted
owls, defined as the number of young fledged
per pair, varies both spatially and temporally
(White et al. 1995). Mexican spotted owls may
have a higher average reproductive rate (1.001
fledged young per pair) than the California
(~0.712; Noon et al. 1992) and the northern
spotted owl (~0.715; Thomas et al. 1993). All
three subspecies exhibit temporal fluctuations in
reproduction, although the amplitude of those
fluctuations may be greatest for the Mexican
spotted owl.
Environmental Environmental Variation
Variation
Environmental conditions greatly affect
reproduction and/or survival of nestlings
through fledging and to adulthood. However,
adult survival rates appear to be relatively constant
across years, as suggested by high pair
persistence rates (White et al. 1995). Such life
history characteristics are common for Kselected
species, for which populations remain
relatively stable even though recruitment rates
might be highly variable. With no recruitment,
the population declines at the rate of 1 minus
adult survival, or the adult mortality rate.
Population Population Trends Trends
Trends
We have inadequate data to estimate population
trends in Mexican spotted owls. We have
little confidence in our estimates of population
trend that include estimates of juvenile survival
because these estimates of juvenile survival are
probably biased low. Further, the population
studies from which parameter estimates were
derived have not been conducted for a sufficiently
long period to capture temporal variation.
Population trend was also evaluated with
Volume I/Part II
33
Mexican Spotted Owl Recovery Plan
occupancy data (White et al. 1995), but again is
suspect. Changes in occupancy rate probably
correspond more with how monitoring of owls
was performed rather than reflecting true change
in the owl population. As a complicating factor,
a nonrandom sample of all existing Mexican
spotted owl territories was monitored, thus
limiting possible inferences.
MOVEMENTS
MOVEMENTS
MOVEMENTS
Seasonal Seasonal Movements Movements
Movements
Seasonal movement patterns of Mexican
spotted owls are variable. Some radio-tracked
owls are year-round residents within an area,
some remain in the same general area but show
shifts in habitat-use patterns, and some migrate
considerable distances (20-50 km [12-31 miles])
during the winter (Ganey and Balda 1989b,
Ganey et al. 1992, Willey 1993, Ganey and
Block unpublished data). In general, migrating
owls move to more open habitats at lower
elevations (Ganey et al. 1992, Willey 1993).
Willey (1993), however, observed one owl that
migrated to coniferous forest at a higher elevation
than the owls’ breeding-season range.
Natal Natal Dispersal
Dispersal
Little is known about habitat use by
juveniles during natal dispersal. Seven juveniles
radio-tracked in southern Utah (Willey 1993)
dispersed over distances ranging from 24 to 145
km (15 to 90 miles). These owls apparently
moved through a variety of habitats including
spruce-fir and mixed-conifer forests, pinyonjuniper
woodland, mountain shrublands, desert
scrublands and desert grasslands. Another five
juvenile owls were radio-tagged in the San Mateo
Mountains of New Mexico in 1993 (Peter
Stacey, Univ. of Nevada, Reno, pers. comm.).
Two of these apparently moved to an adjacent
mountain range before their signals were lost. Of
the remaining three, one was relocated the
following year within the San Mateo Mountains.
Fates of the other two juveniles were unknown.

Volume I/Part II
LANDSCAPE LANDSCAPE LANDSCAPE PATTERN
PATTERN
AND AND METAPOPULATION
METAPOPULATION
STRUCTURE
STRUCTURE
Keitt et al. (1995) examined the spatial
pattern of forest habitat patches across the range
of the Mexican spotted owl. Their objective was
to gauge the extent to which the owl might
behave as a metapopulation in the classical sense
of a set of local populations linked by infrequent
dispersal. Such a finding, if verified, would
suggest that population dynamics of owls in one
local population might be influenced by factors,
including management activities, that affected
nearby populations. Conversely, if local populations
are functionally discrete, then those populations
could be treated separately with some
confidence that actions in one part of the owl’s
range would not greatly affect other populations.
Keitt et al. (1995) concluded that the owl
probably behaves as a classical metapopulation
over much of its range. That is, the level of
habitat connectivity is such that many habitats
are “nearly connected” at distances corresponding
to their best empirical estimates of the owl’s
dispersal capability. At this scale, the landscape
consists of a set of large, more-or-less discrete
habitat clusters. For example, most of the
Mogollon Rim functions as a single cluster, the
southern Rockies as another single cluster, and
so on. This suggests that owls could disperse
within habitat clusters with very high probability,
and disperse between clusters at very low
probability. Thus, we would expect owls to
disperse within clusters most of the time but
between clusters only rarely which is consistent
with the definition of a metapopulation. This
finding suggests that the Plan should incorporate
recommendations that maintain (or increase)
habitat connectivity across the owl’s range.
Habitat connectivity buffers a population from
stochastic variability through time by providing
the opportunity for local population failures to
be “rescued” by immigration from other populations.
Keitt et al. (1995) also attempted to identify
those habitat clusters most important to overall
landscape connectivity. They first ranked habitats
to emphasize the importance of large patches
34
Mexican Spotted Owl Recovery Plan
in the landscape, and second, they modified this
approach to emphasize positional effects (i.e.,
small clusters that are important because they act
as “stepping stones” or bridges between larger
habitat clusters).
In the first analysis, the largely contiguous
habitat of the Mogollon Rim emerged as most
important overall, because of its large area. In the
analysis emphasizing cluster position, a few small
clusters emerged as particularly important. These
included several fragments of the Cibola National
Forest (Mt. Taylor and Zuni Mountains)
that may serve as stepping stones between other,
larger clusters. These small patches may warrant
particular management attention; they may
support few owls but may nevertheless be
important to overall landscape connectivity.
CONCLUSIONS
CONCLUSIONS
In many ways, the Mexican spotted owl
appears to be quite similar to both the northern
and California spotted owls with respect to
general behavioral patterns and ecology. For
example, all three subspecies are most common
in forests of complex structure, prey mainly on
nocturnally-active small mammals, and share
similar vocalizations, reproductive chronologies,
and population characteristics. However, important
differences exist between the Mexican
spotted owl and the other subspecies. The
distributional pattern of the Mexican spotted
owl is more disjunct than that of the other
subspecies, with the possible exception of the
California spotted owl population in the mountain
ranges of southern California (Noon and
McKelvey 1992). The Mexican subspecies also
appears to use a wider range of habitat types
than the other subspecies. These unique aspects
of the ecology of the Mexican spotted owl
require unique approaches to its management.
For example, threats to owl habitat and management
proposed to address those threats may well
differ among the diverse habitats occupied by
Mexican spotted owls. In addition, because of
its’ disjunct distributional pattern, dispersal
among subpopulations of Mexican spotted owls
is an important consideration. Thus, habitat
management plans may need to consider not
only areas occupied by owls but also intervening

areas, even where such areas are very different
in habitat structure from those typically
occupied by spotted owls.
We have learned a great deal about the
Mexican spotted owl in the last decade, but
significant information gaps still remain. Most
studies of the owl to date have been descriptive
rather than experimental (III.D). Although
we have identified patterns with
Volume I/Part II
35
Mexican Spotted Owl Recovery Plan
respect to some aspects of the owls’ ecology (e.g.
habitat use), cause and effect relationships have
not been documented. Further, many aspects of
spotted owl demography and population structure
remain unclear. These considerations
suggest that much additional research is needed,
and that management recommendations in the
near term must deal with high levels of uncertainty.

Volume I/Part II
B. B. RECOVERY RECOVERY UNITS
UNITS
Sarah E. Rinkevich, Joseph L. Ganey, William H. Moir,
Frank P. Howe, Fernando Clemente, and Juan F. Martinez-Montoya
The Mexican spotted owl inhabits diverse
forest types scattered across an even more physically
diverse landscape. Further, human activities
vary dramatically throughout the owl’s range.
These variations limit our ability to approach a
status assessment on a rangewide basis. Consequently,
we divided the range of the owl into
11 geographic areas called “Recovery Units”
(hereafter RUs). Six RUs were recognized within
the United States: Colorado Plateau, Southern
Rocky Mountains - Colorado, Southern Rocky
Mountains - New Mexico, Upper Gila Mountains,
Basin and Range - West, and Basin and
Range - East (Figure. II.B.1). Five RUs were
recognized in Mexico: Sierra Madre Occidental -
Norte, Sierra Madre Oriental - Norte, Sierra
Madre Occidental - Sur, Sierra Madre Oriental -
Sur, and Eje Neovolcanico (Figure. II.B.2).
UNITED UNITED STATES STATES
STATES
Recovery Units were identified based on the
following considerations (in order of importance):
(1) physiographic provinces, (2) biotic
regimes, (3) perceived threats to owls or their
habitat, (4) administrative boundaries, and (5)
known patterns of owl distribution. It is important
to note that owl distributional patterns were
a minor consideration in RU delineation, and
that RUs do not necessarily represent discrete
populations of owls. In fact, movement of
individuals between RUs has been documented
(Ganey and Dick 1995).
Four major physiographic provinces were
used in delineating RUs in the United States: the
Colorado Plateau, Basin and Range, Southern
Rocky Mountains, and Upper Gila Mountains
(Hammond 1965, Wilson 1962, USGS 1970,
Bailey 1980). Biotic regimes were based on
classifications by Bailey (1980) and Brown et al.
(1980). Administrative boundaries were used
where management practices differed between
jurisdictions (e.g., Southern Rocky Mountains
RUs). The following narratives describe dominant
physical and biotic characteristics, patterns
36
Mexican Spotted Owl Recovery Plan
of owl distribution and habitat use, and the
dominant patterns of land ownership and land
use within each RU.
Colorado Colorado Plateau
Plateau
The Colorado Plateau RU (Figure. II.B.3)
coincides with the Colorado Plateau Physiographic
Province (USGS 1970). It includes
most of south-central and southern Utah plus
portions of northern Arizona, northwestern New
Mexico, and southwestern Colorado. Major
landforms include interior basins and high
plateaus dissected by deep canyons, including
the canyons of the Colorado River and its
tributaries (Williams 1986).
Grasslands and shrub-steppes dominate the
Colorado Plateau at lower elevations, but woodlands
and forests dominate the higher elevations
(Bailey 1980, West 1983). Pinyon pine and
various juniper species comprise the primary tree
types in the woodland zone. A montane zone
extends over areas on the high plateaus and
mountains (Bailey 1980). Forest types in this
zone include ponderosa pine, mixed-conifer, and
spruce-fir. Conifers may extend to lower elevations
in canyons. Deciduous woody species
dominate riparian communities, and are most
common along major streams.
The Mexican spotted owl reaches the northwestern
limit of its range in this RU. Owl
habitat appears to be naturally fragmented in
this RU, with most owls found in disjunct
canyon systems or on isolated mountain ranges.
In southern Utah, breeding owls primarily
inhabit deep, steep-walled canyons and hanging
canyons. These canyons are typically surrounded
by terrain that does not appear to support
breeding spotted owls. Owls also apparently
prefer canyon terrain in southwestern Colorado,
particularly in and around Mesa Verde National
Park. In northern Arizona and New Mexico,
owls have been reported in both canyon and
montane situations. Recent records of spotted
owls exist for the Grand Canyon and Kaibab

Figur igur igure igur e II.B.1. II.B.1. Recovery Units within the United States.
Volume I/Part II
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Mexican Spotted Owl Recovery Plan

Figur igur igure igur e II.B.2. II.B.2. II.B.2. Recovery Units within the Republic of Mexico.
Volume I/Part II
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Mexican Spotted Owl Recovery Plan

Figur igur igure igur e II.B.3. II.B.3. Colorado Plateau Recovery Unit.
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Mexican Spotted Owl Recovery Plan

Plateau in Arizona, as well as for the Chuska
Mountains, Black Mesa, Fort Defiance Plateau,
and the Rainbow/Skeleton Plateau on the
Navajo Reservation. In addition, records exist for
the Zuni Mountains and Mount Taylor in New
Mexico.
Federal lands account for 44% of this RU
(Table II.B.1). Tribal lands collectively total
30%, with the largest single entity being the
Navajo Reservation. Private ownership accounts
for 19%, and State lands just 8%. Most Mexican
spotted owls have been located on NPS lands in
this RU, followed by FS and then BLM lands
(Ward et al. 1995).
Recreation ranks first among land uses in
National Parks within this RU. Activities such as
hiking, camping, hunting, rock climbing, and
mountain biking occur in owl habitat. Many of
these activities plus off-road vehicle recreation
also occur on BLM and FS lands throughout the
Colorado Plateau. Various commercial enterprises
relevant to industry and agriculture take
place on these lands. Particularly important are
livestock grazing, timber cutting, coal and
uranium mining, oil and natural gas pumping,
and continued exploration for these and other
resources. Access roads, drill pads, pipelines, and
loading and storage areas accompany all of these
activities.
Southern Southern Rocky Rocky Mountains Mountains - - Colorado
Colorado
This RU (Figure. II.B.4) falls partly within
the Southern Rocky Mountains Physiographic
Province (USGS 1970) and partly within the
Colorado Plateau Ecoregion (Bailey 1980). The
Colorado - New Mexico state line delimits the
southern boundary of this RU because land-use
practices and potential threats on Federal lands
differ between these states. High mountain
ranges characterize the RU (Curtis 1960);
dominant ranges include the San Juan Mountains
of southwestern Colorado, the Sangre de
Cristo Mountains, and the Front Range.
Vegetation ranges from grasslands at low
elevations through pinyon-juniper woodlands,
interior shrublands, ponderosa pine, mixedconifer
and spruce-fir forests, to alpine tundra
on the highest peaks (Daubenmire 1943).
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Mexican Spotted Owl Recovery Plan
The Mexican spotted owl reaches the northeastern
limit of its range in this RU. Found
primarily in canyons in this RU, the owls appear
to occupy two disparate canyon habitat types.
The first is sheer, slick-rock canyons containing
widely scattered patches (up to 1 ha in size) of
mature Douglas-fir in or near canyon bottoms or
high on the canyon walls in short, hanging
canyons. The second consists of steep canyons
containing exposed bedrock cliffs either close to
the canyon floor or, more typically, several tiers
of exposed rock at various heights on the canyon
walls (Reynolds 1993). Mature Douglas-fir,
white fir, and ponderosa pine dominate canyon
bottoms and both north- and east-facing slopes.
Ponderosa pine grows on the more xeric southand
west-facing slopes, with pinyon-juniper
growing on the mesa tops.
Federal lands encompass 55% of the RU,
with the majority administered by the FS,
followed by the BLM and NPS (Table II.B.1).
Approximately 40% of the land is privately
owned, 3% is State administrated, and

41
Table able II.B.1. II.B.1. Land ownership patterns (thousands of hectares) in Recovery Units (RU) within the United States.
LAND AND ST STATUS ST TUS TUS CP CP1
SRM-CO SRM-CO2
SRM-NM SRM-NM3
UGM UGM4
BR-W BR-W5
BR-E
BR-E
Federal Federal Lands
Lands
FS 2,503 5,546 1,220 3,520 2,238 495
BLM 7,672 2,227 520 145 3,359 1,829
NPS 1,678 140 14 17 172 59
Total otal F FFederal
F Federal
ederal 11,853 11,853 11,853
7,913 7,913
1,754 1,754
3,682 3,682
5,769 5,769 2,383
2,383
State State Lands
Lands
AZ 957 0 0 20 2,905 0
NM 300 0 200 192 84 856
UT 862 0 0 0 0 0
CO 11 454 0 0 0 0
Total otal S SState
S tate 2,129 2,129
454 454
200 200
212 212
2,989 2,989 856
856
Tribal Lands 8,026 85 463 941 1,922 382
Private Lands 5,013 5,717 2,141 3,520 3,712 2,586
Other Lands 7 16 105 24 70 1,759 1,101
TOTAL AL AL 27,037 27,037
14,274 14,274
4,582 4,582
8,425 8,425
16,151 16,151 7,308
7,308
1 Colorado Plateau RU
2 Southern Rocky Mountain - Colorado RU
3 Southern Rocky Mountain - New Mexico RU
4 Upper Gila Mountains RU
5 Basin and Range - West RU
6 Basin and Range - East RU
7 Other Lands include U.S. Department of Defense, Bureau of Reclamation, U.S. Fish and Wildlife Service Refuge Lands, etc.
BR-E 6

Figur igur igure igur e II.B.4. II.B.4. Southern Rocky Mountains - Colorado Recovery Unit.
Volume I/Part II
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Mexican Spotted Owl Recovery Plan

Figur igur igure igur e II.B.5. II.B.5. Southern Rocky Mountains - New Mexico Recovery Unit.
Volume I/Part II
43
Mexican Spotted Owl Recovery Plan

Vegetation within the unit has been modified
by past logging, grazing, surface mining,
fuelwood gathering, and fire suppression (Williams
1986, Van Hooser et al. 1993). Ponderosa
pine, mixed-conifer, and spruce-fir forests are
widespread at higher elevations. Juniper savanna
and montane grasslands dominate lower elevations
(Brown et al. 1980). In some areas, mesa
tops dominated by ponderosa pine and juniper
are dissected by steep canyons. Vegetation on
canyon slopes and bottoms includes a variety of
coniferous and deciduous trees.
In general, owls inhabit steep terrain and
canyons in this RU. They typically occur in
mixed-conifer forests on steep slopes in the
Sangre de Cristo Mountains, and in the Jemez
Mountains they occupy canyons incised into
volcanic rock. Patches of mixed-conifer forest
which appear to contain attributes of owl habitat
exist throughout northern New Mexico.
Privately owned lands comprise 47% of the
total land within this RU (Table II.B.1). Federal
lands account for 38%, numerous Pueblos and
Tribal lands 10%, and State-administered lands
4%. Mexican spotted owls have been found
primarily on FS lands, with several records in
Bandelier National Monument as well (Johnson
and Johnson 1985:5).
Dominant land-use practices within this RU
include timber cutting and livestock grazing.
Products such as vigas (small- to mediumdiameter
trees, generally 30-35cm dbh, used for
traditional southwest ceiling beams), latillas
(small-diameter trees, generally 10cm dbh apsen
saplings, used for decorative southwest ceilings
or fences), and fuelwood are harvested for
personal use. Recreational activities in northern
New Mexico include skiing, off-road driving,
hiking, camping, and hunting. Other land uses
include oil, natural gas, and mineral development,
and pipeline corridors.
Upper Upper Gila Gila Mountains
Mountains
The Upper Gila Mountains RU (Figure.
II.B.6) is based on the Upper Gila Mountains
Forest Province (Bailey 1980). Williams (1986)
refers to this area as the Datil-Mogollon Section,
part of a physiographic subdivision transitional
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44
Mexican Spotted Owl Recovery Plan
between the Basin and Range and Colorado
Plateau Provinces. This complex area consists
of steep mountains and deep entrenched river
drainages dissecting high plateaus. The
Mogollon Rim, a prominent fault scarp, bisects
the unit.
McLaughlin (1986) described a “Mogollon”
floral element in this region. The vegetation is a
zonal pattern of grasslands at lower elevations
upward through pinyon-juniper woodlands,
ponderosa pine, mixed-conifer, and spruce-fir
forests at higher elevations. Many canyons
contain stringers of deciduous riparian forests,
particularly at low and middle elevations. This
unit contains the largest contiguous ponderosa
pine forest in North American, an unbroken
band of forest 25 to 40 miles wide and approximately
300 miles long extending from northcentral
Arizona to west-central New Mexico
(Cooper 1960).
Mexican spotted owls are widely distributed
and use a variety of habitats within the Upper
Gila Mountains RU. Owls are most common in
mixed-conifer forests dominated by Douglas-fir
and/or white fir and canyons with varying
degrees of forest cover (Ganey and Balda 1989a,
Ganey and Dick 1995). Owls also occur in
ponderosa pine-Gambel oak forest, where they
are typically found in stands containing welldeveloped
understories of Gambel oak.
Federal lands, mostly FS, encompass 44% of
this RU (Table II.B.1). Tribal lands account for
11%, privately owned lands 42%, and State
lands 3%. The greatest concentration of the
known Mexican spotted owl population occurs
within this RU, and most known owl locations
occur on FS and Tribal lands (Ward et al. 1995).
Many spotted owls are found within wilderness
areas in this RU with the Gila Wilderness
supporting the largest known wilderness population.
The major land use within this RU is timber
harvest. All of the National Forests as well as the
Fort Apache and San Carlos Indian Reservations
have active timber management programs.
Fuelwood harvest, including both personal and
commercial harvest, occurs across much of this
unit. Livestock grazing is ubiquitous on FS lands
and widespread over large portions of the Fort
Apache and San Carlos Indian Reservations. In

45
Figur igur igure igur e II.B.6. II.B.6. Upper Gila Mountains Recovery Unit.

addition, recreational activities such as hiking,
camping, and hunting attract many people to
this RU.
Basin Basin Basin and and Range Range - - West West
West
The Basin and Range Area Province (USGS
1970, Bailey 1980) provided the basis for two
RUs (Figure. II.B.7). We subdivided the Basin
and Range area into eastern and western units
using the Continental Divide as the partition
between these units. The division was based on
differences in climatic and floristic characteristics
between these areas. The Basin and Range - West
flora is dominated by Madrean elements while
the Basin and Range - East unit shows more
Rocky Mountain affinities (Brown et al. 1980).
Geologically, the Basin and Range - West
RU exhibits horst and graben faulting (Wilson
1962) with numerous fault-block mountains
separated by valleys. Complex faulting and
canyon carving define the physical landscape
within these mountains. These ranges include,
but are not limited to, the Chiricahua,
Huachuca, Pinaleno, Bradshaw, Pinal, Santa
Catalina, Santa Rita, Patagonia, Santa Teresa,
Atascosa, Mule, Dragoon, Peloncillo, Mazatzal,
and Rincon Mountains.
Vegetation ranges from desert scrubland and
semi-desert grassland in the valleys upwards to
montane forests. Montane vegetation includes
interior chaparral, encinal woodlands, and
Madrean pine-oak woodlands at low and middle
elevations, with ponderosa pine, mixed-conifer,
and spruce-fir forests at higher elevations (Brown
et al. 1980). Isolated mountain ranges are
surrounded by Sonoran and Chihuahuan desert
basins.
Mexican spotted owls occupy a wide range of
habitat types within this RU. The majority of
owls occur in isolated mountain ranges where
they inhabit encinal oak woodlands, mixedconifer
and pine-oak forests, and rocky canyons
(Ganey and Balda 1989a, Duncan and Taiz
1992, Ganey et al. 1992).
Federal lands encompass 36% of this RU,
mostly administered by the BLM followed by
the FS and a small portion by the NPS (Table
II.B.1). Privately owned lands amount to 22%,
State lands 19%, Tribal lands (San Carlos
Volume I/Part II
46
Apache Reservation) 12%, and DOD lands
11%. Within this RU the Mexican spotted
owl occupies primarily FS lands, and the majority
occur within the Coronado National Forest.
DOD lands also support the owl on Fort
Huachuca Army Base in the Huachuca
Mountains.
Recreation dominates land use within this
unit. Activities such as hiking, birdwatching,
camping, off-road driving, skiing, and hunting
are particularly popular. Livestock grazing is
widespread but most intensive at low and middle
elevations. Urban and rural development and
mining modify portions of the Basin and Range
- West landscape. Timber harvest occurs mainly
on the Prescott National Forest and the San
Carlos Apache Indian Reservation. According to
the Coronado National Forest Land Management
Plan, timber cutting is used sparingly to
enhance wildlife and recreational values. Military
training maneuvers take place in and around
Mexican spotted owl habitat on Fort Huachuca
Army Base.
Basin Basin and and and Range Range - - East
East
Mexican Spotted Owl Recovery Plan
We delineated the Basin and Range - East
RU (Figure. II.B.8) based on the Basin and
Range Area Province (USGS 1970) and the
Desert and Steppic Ecoregions (Bailey 1980).
This RU is characterized by numerous parallel
mountain ranges separated by alluvial valleys and
broad, flat basins. Williams (1986) refers to the
Rio Grande Rift as the separation between the
Basin and Range physiographic province and the
Colorado Plateau and Upper Gila Mountains
physiographic provinces. The climate features
mild winters, as indicated by the presence of
broad-leaved evergreen plants at relatively high
elevations (USDA 1991).
Regional vegetation ranges from Chihuahuan
desert scrubland and Great Basin grasslands
at low elevations, through Great Basin
woodland (pinyon-juniper) at middle elevations
to petran montane coniferous forests at high
elevations (Brown et al. 1980). Montane habitat
includes ponderosa pine, mixed-conifer, and
spruce-fir forests and is patchily distributed
throughout the higher mountain ranges. Cottonwood
bosques as well as other riparian

Figur igur igure igur e II.B.7. II.B.7. Basin and Range - West Recovery Unit.
Volume I/Part II
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Mexican Spotted Owl Recovery Plan

Figur igur igure igur e II.B.8. II.B.8. II.B.8. Basin and Range - East Recovery Unit.
Volume I/Part II
48
Mexican Spotted Owl Recovery Plan

vegetation exist along the Rio Grande corridor.
Montane and especially riparian communities
have been altered considerably by human activities.
Mexican spotted owls occur in the isolated
mountain ranges scattered across this RU. They
are most common in mixed-conifer forest but
are also found in ponderosa pine forest and
pinyon-juniper woodland (Skaggs and Raitt
1988). The owl has been found within mixedconifer
canyon habitat in the Guadalupe Mountains
(McDonald et al. 1991).
Of the Basin and Range - East RU land area,
private lands encompass 35%, Federal lands
48%, State lands 12%, and Tribal lands 5%
(Table II.B.1). The Mescalero Apache Indian
Reservation comprises the largest portion of the
Tribal lands. The majority of known Mexican
spotted owls are located on FS lands, with some
found on NPS and Tribal lands.
Dominant land uses within this RU include
timber management and livestock grazing.
Recreational activities such as off-road driving,
skiing, hiking, camping, and hunting are also
locally common within the RU.
Volume I/Part II
MEXICO
MEXICO
Conserving its natural resources has been a
significant challenge for Mexico. To meet the
challenge, the National System of Protected
Areas was formed; in March of 1988, the General
Law of Ecological Balance and Environmental
Protection was implemented. A total of 5,992
km 2 (almost 600,000 ha) has been decreed as
Protected Natural Areas within the RUs. This
expanse has been classified into nine categories
according to the management objectives and the
legal uses of particular areas. The categories
include: (1) Biosphere Reserves, (2) Special
Biosphere Reserves, (3) National Parks, (4)
National Monuments, (5) National Marine
Parks, (6) Areas of Protection of Natural Resources,
(7) Areas of Protection of Land and
Aquatic Wildlife, (8) Urban Parks, and (9) Areas
Subject to Ecological Conservation. Overall,
there are three types of land tenancy exist in
Mexico: (1) Federal lands, which include
different institutions of the Federal Government
such as Protected Natural Areas; (2) ejidal land,
49
Mexican Spotted Owl Recovery Plan
which includes land allotted by the Mexican
Government to a person or community, for
agriculture, forestry, mining, or other uses; and
(3) private land.
The five RUs in Mexico include Sierra
Madre Occidental - Norte, Sierra Madre Oriental
- Norte, Sierra Madre Occidental -Sur, Sierra
Madre Oriental - Sur, and Eje Neovolcanico
(Figure. II.B.2). Three major physiographic
provinces were used in the delineation: Sierra
Madre Occidental, Sierra Madre Oriental, and
Sistema Volcanico Transversal (Cuanalo et al.
1989). Criteria used to delineate RUs in Mexico
were similar to that used to conform the RUs in
the United States. These criteria, listed in order
of importance, were: (1) distribution of the
spotted owl, (2) local vegetation, (3) physiographic
features, (4) administrative boundaries,
and (5) potential threats to the conservation of
the owl and its habitat.
Owl distribution is disjunct across Mexico.
Williams and Skaggs (1993) report spotted owls
at 53 locations in 11 mainland Mexican States.
Although vegetation types differ throughout
each RU, oak and pine-oak forest types appeared
to be commonly associated with owl habitat in
most or all RUs. These oak species included
Quercus resinosa, Q. gentryi, Q. eduardii, Q.
grisea, Q. chihuahuensis, Q. potosina/Q. laeta, and
Q. coccolobifolia. Further, Pinus teocote was the
most common pine occurring on upper mesas
and occasionally on north-facing slopes in some
areas where owls were found. Land uses within
all RUs include timber cutting, cattle and sheep
grazing, fuelwood gathering, and clearing forested
areas for agriculture. Although, these land
uses are practiced in different amounts throughout
each RU, the majority occur within ejidos.
The following narratives describe dominant
physical and biotic attributes, distribution of
owls, and land administration and ownership
of each unit.
Sierra Sierra Madre Madre Occidental Occidental - - Norte
Norte
Covering an enormous area, the Sierra
Madre Occidental - Norte includes parts of the
States of Chihuahua, Sinaloa, Durango, and
Sonora. In general, this area is characterized by
isolated mountain ranges surrounded by both

narrow and wide valleys. Vegetation communities
consist of pine-oak forest, tropical deciduous
forest, oak forest, microphyll shrub, and grassland.
Mexican spotted owls have been reported in
the northern and western portions of this RU. A
recent study in Sonora found 12 sites in isolated
mountain ranges (Cirett-Galan and Diaz 1993).
The owls occupied canyons and slopes with
various exposures, and most were found in pineoak
forest. In portions of Chihuahua, 25 owls
were located at 13 different localities in several
mountain ranges (Tarango et al. 1994). Most
owls were found in small, isolated patches of
pine-oak forest in canyons.
Records for the State of Sinaloa are limited.
There are at least two records from the high
Rancho Liebre Barranca, near the Sinaloa-
Durango State line (Williams and Skaggs 1993).
These sites were described as deep canyons
containing pine-oak and subtropical vegetation
(Alden 1969).
Private lands comprise 74%, ejidos 25%, and
Federal lands 1% of the total land within this
RU (Table II.B.2). Chihuahua has two National
Parks: Cascadas de Bassaseachic, and Cumbres
de Majalca. This RU also includes La Michilia
Biosphere Reserve, located in Durango. Biosphere
Reserves are protected areas with
relatively unaltered landscapes and contain
endemic, threatened, or endangered species.
Volume I/Part II
Mexican Spotted Owl Recovery Plan
Sierra Sierra Madre Madre Oriental Oriental - - Norte Norte
Norte
Table able II.B.2. II.B.2. Land ownership patterns (thousands of hectares) in Recovery Units within Mexico.
__________________________________________________________________________________________
__________________________________________________________________________________________
Land Land Land Ownership Ownership Ownership SMO SMO SMOcN SMO cN 1 SMO SMOrN SMO rN 2 SMO SMOcS SMO SMOcS
cS 3 SMO SMO SMOrS SMO SMOrS
rS 4 ENV ENV5
_________________________________________________________________________________________
_________________________________________________________________________________________
Ejidos6 4,783 28 1,220 235 441
PNAs7 46 0 38 250 274
Private 14,100 7,506 2,075 1,630 5,306
Total otal 18,929 18,929 7,534 7,534 3,333 3,333 2,115 2,115
6,021
6,021
1 Sierra Madre Occidental - Norte RU
2 Sierra Madre Oriental - Norte RU
3 Sierra Madre Occidental - Sur RU
4 Sierra Madre Oriental - Sur RU
5 Eje Neovolcanico RU
6 Ejidos are lands allocated by the Mexican Government to a person or community, to be
used for agriculture, forestry, mining, etc.
7 Protected Natural Areas
50
The Sierra Madre Oriental - Norte includes
the central portion of the State of Coahuila. This
area is characterized by broad mountain ranges
surrounded by valleys. Vegetation consists of
grasslands, mesquite woodland, dwarf oak
groves, submontane shrubland, desert shrubland,
crasicaule shrub, and pine-oak and oak forests.
Two owl records are reported for this RU. At
one of these sites an owl was observed roosting
in a canyon bottom under a dense canopy of
maples and oaks. Vegetation in the other canyon
was described as “garden-like,” containing pines,
oaks, and madrones (Williams and Skaggs
1993).
Lands in this RU are almost entirely privately
owned (Table II.B.2). Private lands encompass
over 99% and ejidos comprise < 1% of
the total land area. No Protected Natural Areas
of any category exist in this RU.
Sierra Sierra Madre Madre Occidental Occidental Occidental - - Sur
Sur
The Sierra Madre Occidental - Sur RU
includes parts of the States of Durango,
Zacatecas, San Luis Potosi, Aguascalientes,
Jalisco, Nayarit, Queretaro, and Guanajuato. In
general, this area is characterized by isolated

mountains, valleys, and severely dissected canyons
and gorges. Vegetation includes mesquite
woodland, submontane shrub, grasslands, pineoak
forest, crasicaule shrub, low tropical deciduous
forest, and desert shrubland.
Records exist for owls in La Michilia Biosphere
Reserve. In addition, Mexican spotted
owls have recently been found in Aguascalientes
near the border of Zacatecas, in the Sierra Fria
(Williams and Skaggs 1993). Owl records also
exist within Guanajuato State.
Private lands comprise 62%, ejidos 37%, and
Federal lands 1% of this RU (Table II.B.2).
Federal lands include two National Parks: El
Climatario in Queretaro State, and Gogorron in
the State of San Luis Potosi. In addition, this RU
includes Mariposa Monarca Sanctuary, a Special
Biosphere Reserve. The Special Biosphere
Reserves have one or more ecosystems, are
relatively unaltered by anthropogenic activities,
and contain endemic, threatened, or endangered
species.
Sierra Sierra Madre Madre Oriental Oriental Oriental - - Sur
Sur
The Sierra Madre Oriental - Sur includes
parts of the States of Coahuila, Nuevo Leon, and
Tamaulipas. This RU is characterized by long
ridges with sharp pinnacles, narrow valleys, and a
few plateaus. Vegetation consists of pine forest,
submontane shrublands, dwarf oak, and desert
rosetofilo shrublands.
Mexican spotted owls have been found in
the southern portions of Coahuila (Williams and
Skaggs 1993) and in Tamaulipas (Ward et al.
1995). The owls were found in oak, pine,
juniper, and mixed-conifer forests. They were
reported to use cliff sites for nesting and roosting.
Five locations have been reported in Nuevo
Leon. These sites were described as pine-oak and
mixed-conifer forests with large cliffs having
northeast exposures.
Volume I/Part II
51
Mexican Spotted Owl Recovery Plan
This RU is comprised of 77% private property,
12% Federal lands, and 11% ejidos (Table
II.B.2). The Federal lands include one National
Park, Cumbres de Monterrey in Nuevo Leon.
Natural Monument Cerro de la Silla, in Nuevo
Leon, is also within this RU. Natural Monuments
possess one or more elements of national
significance. These elements may be sites or
natural objects that have been placed under
absolute protection because of their unique and
exceptional makeup, aesthetic interest, and/or
historical or scientific value.
Eje Eje Neovolvanico
Neovolvanico
The Eje Neovolcanico RU covers portions
of many States including Jalisco, Michoacan,
Guanajuato, Queretaro, Hidalgo, Mexico,
Guerrero, Puebla, Morelaos, Tlaxcala Veracruz,
and Oaxaca. This RU is characterized by volcanic
cones severely dissected by ravines. The
area also includes rounded hills, slopes, and
plateaus. Vegetation communities include pineoak
forest, grassland, low tropical deciduous
forest, crasicaule shrub, oak forest, juniper forest,
pine forest, mesquite woodlands, and desert
shrublands.
Mexican spotted owls have been reported in
Jalisco on the volcano of Cerro Nevado de
Colima (Voacan de Nieve). Vegetation in this
area consists of pine-oak forest. One Mexican
spotted owl was collected near the city of
Uruapan in the State of Michoacan at Cerro de
Tancitaro. However, this area is now urbanized
and no longer contains owl habitat. Although
other states in this RU appear to contain suitable
owl habitat, Jalisco is the only State known to
have recent records of spotted owls.
This unit is comprised of 88% private lands,
5% Federal lands, and 7% ejidos (Table II.B.2).
This RU includes 19 National Parks, 1 Special
Biosphere Reserve, and 1 Area of Protection of
Land and Aquatic Wildlife.

Volume I/Part II
C. C. DEFINITIONS DEFINITIONS OF OF FOREST FOREST COVER COVER TYPES
TYPES
James L. Dick, Jr., Joseph L. Ganey, and William H. Moir
This Recovery Plan proposes specific
guidelines for several forest cover types, including
mixed-conifer, pine-oak, and riparian forests
(III.B). This is based on: (1) considerable evidence
that these cover types are of specific
importance to the Mexican spotted owl in terms
of providing habitat for nesting, roosting, and
foraging activities (Ganey and Dick 1995); and
(2) the Team’s desire to target guidelines for the
most appropriate habitats and avoid imposing
restrictions where specific guidelines to protect
spotted owl habitat are unwarranted.
Numerous treatments deal with the concepts
of classifying vegetation to cover or habitat types
(e.g., Daubenmire 1952, 1968, Pfister 1989).
These concepts will not be reviewed in any
depth here. In general, we accept the view that
the basic unit of classification of climax vegetation
is the plant association (Küchler 1964,
Daubenmire 1968, Pfister 1989). These associations
are defined using information on present
species composition and successional pathways.
The problem with applying guidelines to plant
associations is that many forests in the southwest
may and should not be in or even near a climax
condition because of the frequency and intensity
of disturbance events in these forests. For example,
in an analysis of Mexican spotted owl
habitat on the Alpine Ranger District, Apache-
Sitgreaves National Forest, the Team determined
that habitat classifications based on current and
climax vegetation gave very different results.
Based on current vegetation, important roosting
and nesting habitat typed out as mixed-conifer
forest, whereas a classification based on potential
natural vegetation (PNV) typed many of these
areas as spruce-fir forest. This points out the
need for clear, operational definitions of cover
types to be used when applying guidelines under
this Plan.
In this section, we first review some of the
relevant literature on forest cover types in the
southwest, and then provide operational definitions
and a simple key that should allow land
managers to classify lands in a manner compatible
with the recommendations provided in this
52
Mexican Spotted Owl Recovery Plan
Plan. Our intent is not to provide a comprehensive
classification scheme here or to supplant
extant classification schemes. Rather, our intent
is to provide guidance to land managers charged
with applying Recovery Plan guidelines and to
facilitate uniform application of guidelines across
administrative boundaries.
LITERATURE LITERATURE REVIEW
REVIEW
Extensive literature exists on both vegetation
classification in general and on classification
systems for southwestern forests. Our intent is
not to review that literature exhaustively, but to
present an overview of some classification
systems currently in use. This information will
provide the background for discussion of forest
type definitions relevant to this Plan.
Soil temperature (STR) and moisture (SMR)
regimes provide one possible approach to classifying
forest types. STR and SMR may be used to
conceptualize three major groups of cover types
in the southwestern United States. Ponderosa
pine forests typically occur where the STR is
frigid or (in southern Arizona and southwestern
New Mexico) mesic and where the SMR is ustic.
Spruce-fir forests everywhere occur on soils of
cryic SMR, whereas mixed-conifer forests are
uniquely udic and frigid in their SMR and STR,
respectively. The implication is that these soil
parameters partition the soil environment into
three mutually exclusive but all encompassing
classes (USDA 1991). These classes are generally
consistent with the three major forest type
groups mentioned.
Most vegetation-classification schemes,
however, are based on either exisiting vegetation
or on a combination of existing vegetation and
knowledge of successional potential (Layser and
Schubert 1979). Eyre (1980) discussed the
practice of defining forest cover types on the
basis of “present occupancy of an area by tree
species.” He further described the practice of
naming forest types after the dominant tree
species. Dominance was determined by relative
proportions of basal area, and the type name was

usually confined to one or two species. An added
requirement was that a species must contribute
at least 20% of the total basal area to be used in
the type name.
Numerous authors have expanded on this
approach, and developed and refined classification
systems for southwestern forests based not
only on existing vegetation but also on estimated
site potential. These treatments are discussed
below.
Ponderosa Ponderosa Pine
Pine
The ponderosa pine forest type occurs in
what Moir (1993) described as the Lower Montane
Coniferous Forest. Forests in this zone are
dominated by pines, sometimes co-occurring
with junipers and oaks. The climate is sometimes
borderline for forests, with moisture becoming
limiting in the upper portions of the soil profile
during part of the long growing season. Moir
(1993) included the following series in this
general forest type: Ponderosa pine - Gambel
oak, Ponderosa pine - silverleaf oak, Ponderosa
pine - pinyon pine - Gambel oak, Ponderosa
pine - pinyon pine - gray oak, and Chihuahua
pine.
Layser and Schubert (1979) described the
Ponderosa Pine Series as being generally dominated
by the Rocky Mountain variety of ponderosa
pine (var. scopulorum), except in southeastern
Arizona, where Pinus ponderosa var. arizonica
dominates. This series occurs in areas that are
generally too warm or too dry for Douglas-fir
and/or true firs. Gambel oak is often a long-lived
seral species. The Ponderosa Pine Series in the
southwest is generally more complex than that
described for the northern Rocky Mountains,
because of the additional associated tree species
and the presence of two varieties of ponderosa
pine (Layser and Schubert 1979). Hanks et al.
(1983), Alexander et al. (1984a), Alexander and
Ronco (1987), DeVelice et al. (1986), and
Fitzhugh et al. (1987) provide further discussion
of the Ponderosa Pine Series and associated
habitat types and phases in the southwestern
United States.
Volume I/Part II
53
Mixed-Conifer
Mixed-Conifer
Mexican Spotted Owl Recovery Plan
Mixed-conifer forests in the southwestern
United States generally approximate to the
Upper Montane Coniferous Forest discussed by
Moir (1993). Mixed-conifer forests are most
common between approximately 2,440 and
3,050 m (8,000-10,000 feet) in elevation, but
may occur higher or lower depending on topography
and aspect. In particular, mixed-conifer
forest may extend to lower elevations in canyon
systems and cold-air drainages.
Southwestern mixed-conifer forests are
among the most complex forest types known,
exhibiting great variation in tree composition
(USDA 1983). Overstory species in these forests
include Rocky Mountain Douglas-fir, white fir,
Rocky Mountain ponderosa pine, quaking
aspen, southwestern white pine, limber pine,
and blue spruce. Forests in any successional stage
may be mixed-conifer if tree regeneration indicates
any of the above tree species will assume
dominance in time. Some stands may consist of
only two species, whereas others may contain as
many as eight associates (USDA 1983). Gambel
oak and/or silverleaf oak may share overstory or
understory dominance with the conifers in
mixed-conifer forests. Again, one of the key
attributes of southwestern mixed-conifer is its
inherent variability and diversity.
At the warm/dry end of the environmental
continuum, mixed-conifer forest typically
intergrades with ponderosa pine forest. Where
Douglas-fir, white fir, or blue spruce, either
singly or in combination, constitute less than
5% cover or are considered “accidental” in late
successional stands, these stands are not included
in the mixed-conifer forest classification.
At the cold/wet end of the environmental
continuum, mixed-conifer forest typically
intergrades with subalpine spruce-fir forest.
Where corkbark fir (Abies lasiocarpa var.
arizonica), subalpine fir (A. lasiocarpa var.
lasiocarpa), or Englemann spruce, either singly
or in common, constitute more than 5% of the
cover or are not considered “accidental,” the
forest is subalpine and no longer considered
mixed-conifer.
In addition to this general description,
numerous authors have discussed aspects of

southwestern mixed-conifer forests or classification
of southwestern forests. Pearson (1931)
described a “Douglas-fir Zone.” He stated that
although Douglas-fir is generally regarded as the
characteristic tree of this type, it rarely occurs in
pure stands. Instead, it commonly occurs in
stands with white fir, limber or Mexican white
pine, and blue spruce. Western yellow pine (e.g.,
ponderosa pine) is common in the lower portion
of the type, and Engelmann spruce is common
in the upper portion. Quaking aspen is common
throughout the type.
Choate (1966) also described Douglas-fir
forests in New Mexico as seldom growing in
pure stands. He also stated that it mixes with
ponderosa pine at lower elevations and with true
firs and spruce at the upper limits. White fir and
quaking aspen are common associates throughout
the Douglas-fir type.
USDA (1992) described old-growth attributes
by cover types, including a “mixedspecies
group” Forest Cover Type, which included
the Douglas-fir, white fir, blue spruce,
and limber pine forest cover types. They described
these mixed-species stands as having a
rich diversity of vegetation, typically including at
least three tree species.
Moir (1993) described mixed-conifer forests
as upper montane coniferous forests featuring
Douglas-fir, white fir, several tall pine species,
blue spruce, and quaking aspen. He included the
following series in this general forest type: Blue
Spruce, White fir - Douglas-fir, Douglas-fir -
Southwestern White Pine, White Fir - Douglasfir
- Ponderosa Pine, Douglas-fir - Limber Pine -
Bristlecone Pine, Douglas-fir - Gambel Oak, and
Douglas-fir - Silverleaf Oak. These forests are
very productive because of ample precipitation
and soils that are well watered throughout the
long growing season.
Fletcher and Hollis (1994) described mixedconifer
forest cover types as those dominated by
Douglas-fir and/or white fir, usually containing
varying amounts of ponderosa pine, southwestern
white pine, and/or limber pine. Hardwood
species, including rocky mountain maple (Acer
glabrum), boxelder (A. negundo), bigtooth maple
(A. grandidentatum), Gambel oak, quaking
aspen, and other hardwood species may also be
present. Douglas-fir and/or white fir typically
Volume I/Part II
54
Mexican Spotted Owl Recovery Plan
comprise at least 40 percent and hardwood
species less than 40 percent of the stand basal
area. Conifers typical of higher elevations, such
as Engelmann spruce, blue spruce, and/or subalpine
fir may occur as “accidentals,” or provide
less than about 5% cover in late successional
stands.
Layser and Schubert (1979), Moir and
Ludwig (1979), Alexander et al. (1984a, b),
Alexander and Ronco (1987), Youngblood and
Mauk (1985), DeVelice et al. (1986), and
Fitzhugh et al. (1987) all discussed classification
of forest types in general or mixed-conifer forest
types in particular in the southwestern United
States. These treatments vary somewhat, possibly
because of regional differences in forest types. A
general consensus, however, indicates that
mixed-conifer forest types generally fall in the
following four series: Abies concolor, Psuedotsuga
menziesii, Pinus flexilis, or Picea pungens.
Spruce-Fir
Spruce-Fir
Spruce-fir forests in the southwestern United
States generally coincide with the Subalpine
Coniferous Forest discussed by Moir (1993).
These are high-elevation forests occurring on
cold sites. They have short growing seasons,
heavy snow accumulations, and strong ecological
and floristic affinities to cold forests of higher
latitudes. Dominant trees include Engelmann
spruce, subalpine and/or corkbark fir, or sometimes
bristlecone pine. Moir and Ludwig (1979)
included the Picea engelmannii and Abies
lasiocarpa Series in the general spruce-fir forest
type. Moir (1993) included the following series
in this general forest group: Bristlecone pine,
Engelmann spruce - bristlecone pine, corkbark
fir - Engelmann spruce, Corkbark fir - Engelmann
spruce - white fir, Engelmann spruce -
Douglas-fir, and Engelmann spruce - limber
pine.
Other Other Forest Forest Types Types of of Interest
Interest
Chihuahua Chihuahua Pine
Pine
The Pinus leiophylla Series is described by
Layser and Schubert (1979). This series typically

contains a diverse mixture of conifers and
evergreen oaks. The conifer component is
extensive enough to characterize this series as
forest rather than woodland. Dominant conifers
are typically Chihuahua pine, Apache pine, and
P. ponderosa var. arizonica (Layser and Schubert
1979). This series is Madrean in affinity and,
within the U.S., is restricted to central and
southern Arizona and southwestern New Mexico
(Brown et al. 1980). Moir (1993) included this
type in the Lower Montane Coniferous Forest
group.
Quaking Quaking Quaking Aspen
Aspen
Quaking aspen is a special feature of western
landscapes. It is a major seral species in the
following series; Abies lasiocarpa, Picea pungens,
and Abies concolor. It is a minor seral species in
the Picea engelmannii, Pseudotsuga menziesii, and
Pinus ponderosa Series (Larson and Moir 1986).
As such, quaking aspen should be a common
component of these landscapes under natural
disturbance regimes.
Riparian Riparian Forests
Forests
Numerous authors have discussed classification
and ecology of riparian forests in the southwestern
United States (e.g., Pase and Layser
1977, Layser and Schubert 1979, Brown et al.
1980, Medina 1986, Szaro 1989). In general,
southwestern riparian forests are dominated by
various species of broadleaved deciduous trees
and shrubs. Trees common in adjacent uplands,
such as conifers, oaks, and quaking aspen, may
occur in association with riparian trees, but
generally do not dominate the site (Brown
1982).
PLAN PLAN DEFINITIONS
DEFINITIONS
Our classification scheme is primarily
concerned with a subset of the available forest
types in the southwestern United States. We are
interested in both potential and existing vegetation.
Consequently, our scheme is a hybrid of
classification schemes based on potential vegetation
(series, association and habitat type) and
forest cover types based on existing vegetation.
Volume I/Part II
55
Mexican Spotted Owl Recovery Plan
Three terms used in our definitions require
clarification here. These are “pure,” “majority,”
and “plurality.” Various definitions exist to
describe what constitutes a pure stand. Daniel et
al. (1979) described pure stands as those where
>90% of the dominant or codominant trees are
of a single species. A stand may have an understory
of other species without changing the pure
designation. The key to this concept is the
distinction between the dominant and codominant
species and the understory component. In
contrast, Eyre (1980) defined a pure stand as one
where >80% of the stocking is by one species.
For purposes of this plan, we use the term
pure to refer to any stand where a single species
contributes >80% of the basal area of dominant
and codominant trees. We use the term majority
to refer to the situation where a single species
contributes >50% of the basal area (Eyre 1980).
We use the term plurality to refer to the situation
where a species (or group of species of
interest) comprises the largest proportion of a
mixed-species stand (Eyre 1980).
With these definitions and concepts in
mind, definitions for specific forest cover types
are provided below.
Ponderosa Ponderosa Pine Pine Forest
Forest
as:
We define the Ponderosa Pine Forest Type
1. Any forested stand of the Pinus ponderosa
Series not included in the Pine-Oak
Forest Type (see below), or;
2. Any stand that qualifies as pure (Eyre
1980) ponderosa pine, regardless of the
series or habitat type.
Pine-oak Pine-oak Forest
Forest
A number of habitat types exist in the
southwestern United States that could be described
as pine-oak. Most of the stands relevant
to recovery of the Mexican spotted owl fall
within two series, the Pinus ponderosa Series and
the Pinus leiophylla Series. Present evidence,
however, suggests that the former series includes

many areas that could never attain the type of
forest structure sought by spotted owls for
roosting and nesting. Therefore, in an attempt to
avoid needlessly restricting management options
on lands not used to any great extent by the
spotted owl, we propose the following operational
definition for pine-oak forest under this
Plan:
1. Any stand within the Pinus leiophylla
Series.
2. Any stand within the Pinus ponderosa
Series that meets the following criteria
simultaneously:
Volume I/Part II
a) Habitat types that reflect Quercus
gambelii or a Quercus gambelii phase
of the habitat type.
b) The stand is located in either the
Upper Gila Mountains Recovery
Unit, the Basin and Range-West
Recovery Unit, or the Zuni Mountains
or Mount Taylor regions of the
Colorado Plateau Recovery Unit.
c) >10% of the stand basal area or
2.3 m 2 /ha (10 ft 2 /ac) of basal area
consists of Gambel oak > 13 cm
(5 in) diameter at root collar.
3. Any stand within the Basin and Range-
West Recovery Unit of any other series
that meets the following criteria
simultaneously:
a) A plurality (Eyre 1980) of the basal
area exists in yellow pines (ponderosa,
Arizona, Apache, or Chihuahua).
b) >10% of the stand basal area or
2.3 m 2 /ha (10 ft 2 /ac) of basal area
consists of any oaks > 13 cm (5 in)
diameter at root collar.
56
Mixed-conifer Mixed-conifer Forest
Forest
Mexican Spotted Owl Recovery Plan
Natural variability is high within this forest
type and has been increased by both natural and
human-caused disturbances. Despite this variability,
an extant classification scheme based on
series and habitat types (Hanks et al. 1983,
Layser and Schubert 1979, Alexander et al. 1984
a, b; Alexander and Ronco 1987, Youngblood
and Mauk 1985, DeVelice et al. 1986, Fitzhugh
et al. 1987) is available. This classification system
is in widespread use and has multiple-agency
support. Given that background, we propose
using that system as a starting point in defining
mixed-conifer forest, with some added refinements.
Specifically, we propose that:
1. The definition of mixed-conifer forest
generally be confined to the following
series (Layser and Schubert 1979) and
associated habitat types (after authors
listed above): Abies concolor, Pseudotsuga
menziesii, Pinus flexilis, or Picea pungens.
Within this framework, we provide the
following exceptions to the general guideline
listed above:
1. Any stand within the Pinus aristata,
Picea engelmannii, or Abies lasiocarpa
Series not having a plurality (Eyre 1980)
of basal area of any of Pinus aristata,
Picea engelmannii, Abies lasiocarpa, or
Pinus ponderosa, singly or in combination,
should also be defined as mixedconifer.
2. Stands that can be described as “pure” for
coniferous species other than Douglasfir,
white fir, southwestern white pine,
limber pine, or blue spruce should be
excluded from the broad category of
mixed-conifer for the purposes of Plan
implementation regardless of the series
or habitat type. By pure, we mean that
one species comprises 80% or more of
the dominant and codominant trees
(Eyre 1980).

3. Stands of mixed species with >50% of
the basal area consisting of quaking
aspen should be defined as quaking
aspen for the purposes of Plan implementation
regardless of the series or
habitat type.
High-elevation High-elevation Forests,
Forests,
Including Including Spruce-fir Spruce-fir Forest
Forest
We define this forest type as:
1. Any stand of the Pinus aristata, Picea
engelmannii, or Abies lasiocarpa Series
that meets the following criteria:
Volume I/Part II
a) The majority (Eyre 1980) of stand
basal area consists of any of the three
species listed above, either singly or
in combination, or;
b) Any stand that qualifies as a pure
stand (Eyre 1980) of any of these
species, regardless of the series or
habitat type.
Quaking Quaking Quaking Aspen
Aspen
We propose that any stands with >50% of
the basal area consisting of quaking aspen be
defined as quaking aspen.
KEY KEY TO TO FOREST FOREST COVER COVER TYPES
TYPES
1. Trees deciduous and broadleaved, often
confined to floodplain, drainageway, or
canyon bottom (Layser and Schubert
1979) . . . . . . . . . . . . . . Ripar Riparian Ripar ian F FFor
F For
or orest or est
1. Dominant trees evergreen and needleleaved
.. . . . . . . . . . . . . . . . . . . . . . . . ..2
2. Series = Psuedotsuga menziesii, Abies
concolor, Pinus flexilis, or Picea
pungens . . . . . . . . . . . . . . . . . . . . . .3
2. Series not as above . . . . . . . . . . . . .5
57
Mexican Spotted Owl Recovery Plan
3. >80% of dominant and codominant
trees are species other than Pseudotsuga
menziesii, Abies concolor, Pinus
strobiformis, Pinus flexilis, or Picea
pungens . . . . . . . . Classify Classify bb
by bb
y dominant
dominant
species
species
3. Stand not as above . . . . . . . . . . . . . . . .4
4. Populus tremuloides contributes
>50% of stand basal area
. . . . . . . . . . Quaking uaking Aspen Aspen F FFor
F or orest or est
4. Not as above. . . . . . . Mix ix ixed-conifer ix ed-conifer
For or orest or est
5. Series = Pinus leiophylla . . . . . Pine-oak ine-oak
For or or orest orest
est
5. Series not as above . . . . . . . . . . . . . . . . 6
6. Series = Pinus ponderosa . . . . . . . . . 7
6. Series not as above . . . . . . . . . . . . 10
7. Habitat type or phase includes Quercus
gambelii . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Not as above. . . . . . . . . . . . . .Ponder onder onderosa onder osa
Pine ine F FFor
F or orest or est
8. Area is located within Upper Gila
Mountains Recovery Unit, Basin and
Range-West Recovery Unit, or the
southeastern portion of the Colorado
Plateau Recovery Unit (Zuni Mtns.,
Mt. Taylor). . . . . . . . . . . . . . . . . . . 9
8. Area not located as above. . . . . . . . . .
. . . .. . . . . . . Ponder onder onder onderosa onder osa P PPine
P ine F FFor
F or orest or est
9. >10% of stand basal area or 2.3 m2 /ha
(10 ft2 /ac) consists of Quercus gambelii >
13 cm (5 in) diameter at root collar. . . .
Pine-oak ine-oak F FFor
F or orest or est
9. Not as above . . . . . . . . . . . . . Ponder onder onderosa onder osa
Pine ine F FFor
F or orest orest
est

Volume I/Part II
10. Series = Pinus aristata, Picea
engelmannii, or Abies lasiocarpa
. . . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Series not as above . . . . . . . . . . . 13
11. Stand can be defined as pure for either
Pinus aristata, Picea engelmannii, or Abies
lasiocarpa . . . . . . . . . . SS
Spr S pr pruce-fir pr uce-fir F FFor
F or orest or est
11. Stand not as above . . . . . . . . . . . . . . . 12
12. Pinus aristata, Picea engelmannii,
or Abies lasiocarpa contribute >50%
of stand basal area, either singly or
in combination. . . . . . . S SSpr
S pr pruce-fir pr uce-fir
For or orest or est
12. Stand not as above . . . . . . . . . . . . .
. . . . . . . . . . .Mix ix ixed-conifer ix ed-conifer F FFor
F or orest or est
58
Mexican Spotted Owl Recovery Plan
13. Stand located in Basin and Range-West
Recovery Unit . . . . . . . . . . . . . . . . . . 14
13. Stand not located as above . . . . . . Other ther
14. A plurality of stand basal area is
contributed by Pinus ponderosa,
Pinus engelmannii, or Pinus
leiophylla, either singly or in
combination . . . . . . . . . . . . . . . . .15
14. Stand not as above . . . . . . . . . Other ther
15. >10% of stand basal area or 2.3 m2 /ha
(10ft2 ac) consists of any oak > 13 cm (5
in) diameter at root collar. . . . . . . . . . . .
. .. . . . . . . . . . . . . . . . . PP
Pine-oak P ine-oak F FFor
F For
or orest or est
15. Stand not as above . . . . . . . . . . . . Other ther

The goal of this Recovery Plan is to recover
the Mexican spotted owl so that it no longer
requires protection under the Endangered
Species Act. We submit that this can be best
achieved by ensuring a mosaic of all successional
stages, now and in the future, throughout a
landscape comprised of all known habitat types
used by the owl. In mixed-conifer, pine-oak and
riparian forests, this habitat mosaic must contain
stands adequate for all life-history requirements,
including nesting and roosting.
We agree with the widely held belief that
conditions within some southwestern forests
deviate substantially from those existing prior to
European settlement. Moreover, forests throughout
the U.S. range of the owl are at high risk
from fire, insects, and disease. The mechanisms
responsible for current condition are not completely
known, but synergistic effects of past
timber harvest, overgrazing, and fire suppression
are plausible explanations. The intent of this
Recovery Plan is not to cast blame on any
particular aspect of past management, but to
outline the appropriate steps needed to ensure
persistence of the Mexican spotted owl. Thus,
the basis to maintain owl populations is to
ensure that adequate habitat quality and quantity
will be sustained through time. These conditions
also must be within the natural range of variation.
We recognize, however, that major knowledge
gaps preclude accurate descriptions of the
natural range of variation and presettlement
conditions. We cannot verify that fewer owls
exist today than 100 years ago, or vice versa. We
know little about habitat quality and how
contemporary landscapes and ecosystem conditions
contribute to owl fitness and population
persistence. Thus, management of the owl
should proceed in an iterative fashion. We must
use the best available knowledge to guide current
management, recognizing that new information
from research and monitoring is critical for the
development of long-term management plans.
Volume I/Part II
Mexican Spotted Owl Recovery Plan
D. D. CONCEPTUAL CONCEPTUAL FRAMEWORK FRAMEWORK FOR FOR RECOVERY
RECOVERY
William H. Moir, James L. Dick Jr., William M.
Block, James P. Ward Jr., Robert Vahle,
Frank P. Howe, and Joseph L. Ganey
59
This Recovery Plan details a short-term (10-
15 years) strategy aimed at maintaining owl
habitat where it exists and initiating a process to
develop a forested landscape that includes
replacement habitat. We presently have insufficient
knowledge to design a strategy that will
answer all long-term considerations, such as
allocation of stand structures in space and time.
Under proposed delisting criteria (III.A), the owl
could be delisted within this 10-15 years, rendering
this plan obsolete.
To achieve the recovery goals outlined in this
Plan, management must emulate natural ecosystem
processes and landscape mosaics that balance
natural variability and secure the landscape
against catastrophic habitat loss. Our recommendations
assume that population status and
habitat condition will be monitored in conjunction
with recovery efforts for the Mexican
spotted owl (Part III). The management recommendations
are not meant to stand alone without
such monitoring.
ECOSYSTEM ECOSYSTEM OR OR LANDSCAPE
LANDSCAPE
MANAGEMENT
MANAGEMENT
Volume 2 summarizes current knowledge of
the Mexican spotted owl’s basic natural and life
histories, but a brief reiteration is appropriate
here. First, the owl is found in a number of
different habitat types ranging from slickrock
canyons to cool, mesic forests. Second, the owl
has relatively large home ranges, typically containing
mosaics of vegetation types and different
seral stages and conditions within those types.
Third, the owl takes numerous species of prey
and each of these species has unique habitat
requirements. These factors considered simultaneously
stress the need to consider management
across spatial scales ranging from sites to landscapes
and to provide the diversity of conditions
required for the owl’s life history. Consequently,
we submit that management for Mexican spotted
owls must be viewed within the context of
managing ecosystems.

How can ecosystem management be applied
to the Mexican spotted owl? Ecosystem management
should sustain biotic diversity and the
natural processes and landscape mosaics that
generate that diversity (cf., Jensen and
Bourgeron 1993, Franklin 1993, 1994; Diaz
and Apostol 1993, Kaufmann et al. 1994,
Williams 1994). The current emphasis in
ecosystem management is to use the filter
approach described by Hunter (1991). Two
“sizes” of filters, coarse and fine, are used.
The objective of the coarse filter approach is
to maintain the natural array of conditions that
exist within the biotic and physical limits of the
landscape. This would include special as well as
common habitats. Ideally, the array of conditions
provided by using the coarse-filter approach
should maintain most plants and animals
adapted to natural conditions (Hunter 1991).
This should include most of the habitat conditions
needed by the owl and its prey.
In some cases, however, a fine filter may be
required for specific habitats, or habitat elements,
that fall through the coarse filter. With
respect to the Mexican spotted owl, the coarse
filter is probably sufficient for most foraging
habitats, but a fine filter may be needed to
provide nest and roost sites. For example, the
owl prefers or needs particular landforms (such
as steep-walled canyons), particular structures
(including snags, large trees, large logs, cavities
and other platforms for nesting), mature forests,
and specialized microhabitats. Thus, a fine-filter
analysis is required to identify and ensure continuing
availability of the owl’s specific habitat
needs.
In summary, the coarse filter approach is
used to manage the overall landscape, and, if
properly applied, should suffice to maintain the
natural array of conditions on that landscape.
The fine filter is used to provide specialized
habitats or habitat elements within that overall
landscape.
Two themes of the recovery measures are
consistent with these principles of ecosystem
management. The first theme is that the general
recommendations of this Recovery Plan provide
conditions for the owl across the landscape. This
landscape should provide nesting, roosting,
foraging, and dispersal macrohabitats in the
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Mexican Spotted Owl Recovery Plan
short term. This theme emphasizes protecting
and monitoring owl populations and habitats.
The second theme acknowledges that ecosystems
are temporally dynamic, and that provisions
are needed to ensure owl habitat in the
long term. As nest sites change and are abandoned,
new nest sites should develop and become
occupied. Allocation of mid- to late-seral
forests needed by spotted owls, and other species,
in future decades requires knowledge of
forest disturbances, risks, and rates of succession
at different spatio-temporal scales. We outline
below some disturbances, risks, and tools that
should be considered in managing present and
future owl habitat.
Fire
Fire
Fire is the most rapidly acting of natural
disturbances. A crown fire can quickly consume
forests across vast tracts. After a large crown fire,
habitat components for nesting, roosting, and
foraging are reduced or eliminated. Small-scale
natural fires and prescribed burns, however, can
reduce fuel loadings and create small openings
and thinned stands that increase horizontal
diversity and reduce the spread of catastrophic
fire. Small-scale fires and lightning also create
snags, canopy gaps, and large logs, plus they
perpetuate understory shrubs, grasses, and forbs
which are important habitat components to the
owl, its prey, and other wildlife. Under natural
fire regimes prior to 1890 these small fires
occurred frequently (Moody et al. 1992).
The risk of catastrophic fires is widespread in
Southwestern forests and woodlands (Moody et
al 1992). Fuel accumulations and forests overstocked
with trees place spotted owl habitat at
risk with respect to stand-replacing fires. Figures
II.D.1-3 show the changing fire record from
1910 to 1992, based on records compiled at the
FS Southwestern Regional Office. Because FS
burn policies changed during this period and the
use of prescribed natural fire increased, interpretation
of these records is not straightforward. In
general, however, the figures document an
increase in both area burned per year and in area
lost to catastrophic, stand-replacing fires.
The number of total natural and humancaused
fires generally declined after 1981 (Figure

II.D.1), but the number of large fires (> 4 ha
[>10 acres]) increased at the same time (Figure
II.D.2). Figure II.D.3 shows the trend clearly;
from 1985 to 1992 the number of hectares that
burned increased. If the influence of two exceptional
fire years (1974 and 1979) is removed, the
trend shown in Figure II.D.3 remains; that is,
the number of large fires increased.
Moody et al. (1992) estimated that about
303,500 ha [750,000 acres] of mixed-conifer
forest within FS Region 3 needed treatment to
reduce fire risk in the next 10 years. Unmanaged
and unplanned conversion of large areas of
forests or woodlands to early seral conditions by
wildfire can disrupt management goals to maintain
existing and to provide future spotted owl
habitat (USDA 1993c).
Characteristics of many nest and roost sites
of spotted owls place them at high fire risk.
Some nest/roost locations at special topographic
locations (such as steep-walled canyons or
isolated places) may be fire refugia, however.
Taking cue from these, one promising management
tactic is to isolate nest/roost sites from the
adjoining high-risk forest by reducing flammability
and fire spread in a buffer around the site.
This must be done, of course, without compromising
the site itself as nest/roost habitat.
Inevitably, severe climatic conditions will
occur in the future, and extreme fire years are
possible (Swetnam and Betancourt 1990). Given
the present conditions of Southwestern forests,
extreme fire years could result in holocaustic fires
throughout large portions of the owl’s range.
Because the resulting damage to owl habitat
would be irreparable in the forseeable future,
efforts to limit large-scale catastrophic fires are of
utmost importance for owl conservation.
Increased use of fire and other tools will be
needed to reduce the amount of forest at high
risk from stand-replacing fires. The Recovery
Team encourages proactive fire management
programs which assume active roles in fuels
management and understanding the ecological
role of fire. An example of such a program is the
one employed by the Gila National Forest.
The Recovery Team recognizes that fire
technology may not be at the level of sophistication
needed to maintain owl habitat and create
new habitat. Although we advocate broadscale
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Mexican Spotted Owl Recovery Plan
use of fire in the Southwest, we also stress the
need to approach the use of fire in an adaptive
management context. Prescriptions that maintain
key structural features of owl and small prey
habitats should be developed and tested. These
features include large trees (which are often fire
resistant), snags, logs, and understory hardwood
trees. Treatments to produce or maintain such
habitat components must be assessed by monitoring
to evaluate if treatment objectives were
met in both short and long terms. Wholesale use
of fire without understanding or monitoring its
effects on habitat may render areas unusable by
owls, and may also miss opportunities to improve
our knowledge of fire effects. Fire and
wildlife personnel should work together to refine
fire prescriptions compatible with maintenance
of important habitat elements.
Other Other Natural Natural Disturbances
Disturbances
Disturbances
The vegetative communities that provide
habitat for the Mexican spotted owl are dynamic
assemblages of living plants, snags, logs, and
numerous organisms active in decay and nutrient-cycling
processes. Herbivory, disease, and
structural change caused by bacteria, fungi,
insects, and vertebrates are natural agents of
change in forest and woodland communities and
occur at scales ranging from individual trees to
landscapes.
These disturbances contribute to the formation
of complex landscape mosaics in which
woodlands and forests consist of aggregates of
transient patches and gaps. Added to this patchiness
are changes of the structural elements of owl
habitat caused by disturbances at scales larger
than gaps. Climate change, pollutants, and other
extensive events will produce effects of magnitudes
that are poorly understood (Davis 1989).
Although management scarcely influences the
primary determinants of vegetation pattern
(geology, climate, and genetics), management
can affect vegetation by manipulating the extent,
severity, and frequency of disturbance.
Land managers should recognize that natural
disturbances can create and maintain diverse and
productive ecosystems that always include,
somewhere on the landscape, an adequate
amount and distribution of the vegetative

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Mexican Spotted Owl Recovery Plan
Figur igur igure igur e II.D.1. II.D.1. Historical record of number of total fires and number of natural fires. Data from
USFS Southwestern Region.
Figur igur igure igur e II.D.2. II.D.2. Historical record of fires over four hectares in size. Shown are numbers of fires and
area burned. Data from USFS Southwestern Region.
62

Volume I/Part II
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e II.D.3. II.D.3. Five-year running averages of area burned. Data from USFS Southwestern Region
elements that are the required habitat for the
Mexican spotted owl. The word “adequate” is
crucial. Adequacy is derived from publicly
acceptable landscape descriptions (desired
conditions), together with use of the best succession,
allocation, and landscape-dynamic models
to guide managers in how to get there. Adequacy
is tested by ongoing monitoring and adaptive
management (III.C) and should not be assumed
in the absence of monitoring.
Insects and microorganisms can be beneficial
as well as destructive agents of plant succession
(Dinoor and Eshed 1984, Knauer 1988,
Dickman 1992, Haack and Byler 1993). These
organisms may produce large-scale community
changes after periods of climatic stress that
“predispose” forests to insects or pathogenic
occurrences (Colhoun 1979). Several groups of
forest insects occasionally develop epidemic
populations that severely damage mature forest
trees over large areas. Among the defoliating
insects, the western spruce budworm kills
understory white fir and Douglas-fir and thins
the crowns of overstory trees (Archambault et al.
1994). Outbreaks of western spruce budworm
63
occur every decade or so and extend widely
across the landscape. Perhaps as a response to fire
exclusion policies, recent budworm outbreaks
have tended to be regionally synchronous with
the maturing of host species over large areas
(Swetnam and Lynch 1993). As a complicating
factor, trees that suffer declining vigor from
multiple years of defoliation by budworms may
lose their resistance to more injurious woodboring
insects and ultimately die. Bark beetles
are important wood-boring insects in pinyon,
ponderosa pine, Douglas-fir, and Englemann
spruce. During outbreaks (about every 7 to 10
years), these insects kill groups of mature trees.
In longer outbreaks (usually those following
droughts), mortality groups coalesce and damage
appears to be widespread. Bark beetle populations
are most likely to increase where host trees
are stressed as a result of sublethal fire damage,
dwarf mistletoe infection, or where abundant
green slash is available from thinning or
blowdown.
The principal forest pathogens are root
disease fungi and dwarf mistletoe. Armillaria
root disease is widespread across the forests of

the Southwest. In a few locations it behaves as an
aggressive killing agent (Marsden et al. 1993),
but in most stands it acts to remove trees weakened
by lightning or insects. Other root diseases
are caused by Heterobasidion annosum and
Phellinus schweinitzii.
The most common tree disease in Southwestern
forests is caused by parasitic seed plants
of the genus Arceuthobium, the dwarf mistletoes.
About one-half to two-thirds of the stands in
these forests are infested by dwarf mistletoe.
Infected trees become stunted, develop witches’
brooms, and are eventually killed by this or
other mortality agents. Both root disease and
mistletoe typically occur as “centers” or “patches”
and create slowly but continously expanding
canopy gaps. These agents increase ecosystem
diversity by producing snags, logs, and, in the
case of mistletoe, witches brooms. They also act
synergistically with forest insects.
The relationship between fire and dwarf
mistletoe is complex. Brooms caused by dwarf
mistletoe provide fuel continuity from ground to
tree crown. By maintaining seral trees in forest
stands, fire increases the opportunity for mistletoe
infection because the seral trees are more
commonly hosts than climax trees. Similar
complex relationships exist between fire, bark
beetles, and western spruce budworms.
White pine blister rust is caused by an exotic
fungus that was recently introduced into the
Sacramento Mountains. It has the potential to
kill most of the southwestern white pine in the
mixed-conifer forests (Hawksworth and Conklin
1990) where the greatest concentration of
Mexican spotted owls occurs. Although southwestern
white pine is seldom the most frequent
tree species of a stand, it is an important seral,
dominant, or codominant species in most areas.
This tree produces large seeds and readily fills
gaps opened by mortality of other trees to
budworm, bark beetles, root disease, and mistletoe.
Therefore, the short-term effects of white
pine blister rust may be negative, since a strong
reordering of forest tree composition may take
place. A number of actions can be taken to
“control” the rust and reduce its impacts, but
they are expensive and their effectiveness and
possible side effects are unknown. In the longterm,
a genetic balance between the rust and
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Mexican Spotted Owl Recovery Plan
white pines may occur, as it did with Pinus
monticola in the northern Rockies (Ledig 1992).
Various other arthropods and saprophytic
fungi are also important agents of deterioration
and decay of snags and logs. Although these
agents generally do not kill trees directly, their
activity (decay) can lead to stem breakage and
tree death. They are thus important in determining
the condition and persistence of coarse
woody debris within forest stands.
The cumulative impacts of these disturbance
agents on owl habitat depends on a number of
factors, some of which are subject to manipulation.
In general, these and other kinds of disturbances
affect forest nutrient and water cycles,
solar penetration to the understory, and plant
and animal food webs. The response of understory
vegetation, fungal-small mammal relationships
(Maser et al. 1978), and owl prey to
various disturbance factors can be positive or
negative, depending on numerous site factors
and the successional stage of the affected vegetation.
Because these processes are interactive and
affect a number of vegetation attributes, simple
assessments are inadequate. Several vegetation
management tools, including various kinds of
silviculture, risk-abatement for fire or insect/
disease damage, prescribed burning, and direct
population control are appropriate in various
combinations.
These disturbance agents should be considered
in developing management strategies for
owl recovery. Managers must recognize that the
organisms discussed above and their effects are
not necessarily or even primarily bad. Certain
natural processes may interfere with short-term
priorities of forest management; but the perpetuation
of forest conditions that support those
priorities may depend on natural processes
continuing in the long term. Moreover, conflicting
priorities, or even second- or third-level
priorities may benefit from these organisms.
Evaluations should be based on the role these
organisms play in directing succession toward, or
away from, desired future conditions at different
spatiotemporal scales.
Managers, in consultation with specialists,
can use these organisms to strategic advantage in
creating, enhancing, or maintaining habitats for
owls (and associated biota) in accord with

landscape goals. For example, dwarf mistletoe
creates nest sites for owls in Douglas-fir. In some
places, outbreaks of western spruce budworm
eliminate understory host trees, helping to
reduce fuel ladders that carry fires into tree
crowns. These biotic agents of mortality have
thinning effects on tree overstories. Such thinning
affects nutrient and hydrological cycles,
understory vegetation, and availability of prey to
owls.
In summary, we encourage resource managers
to work with forest insect and disease specialists
to develop ecological assessments of these
kinds of disturbances at various scales
(Kaufmann et al. 1994). Understanding the
scientific basis of forest change and evolution is
crucial to successful management of forest
ecosystems, and therefore to recovery of the
spotted owl.
Degradation Degradation of of of Riparian Riparian Forests
Forests
Riparian forests may also function as important
components of ecosystems supporting
spotted owls. These communities, particularly
mature, multi-layered forests, could be important
linkages between otherwise isolated subpopulations
of spotted owls. They may serve as
direct avenues of movement between mountain
ranges or as stopover sites where drainages bisect
large expanses of landscape that otherwise would
be inhospitable to dispersing owls. Further,
historical evidence exists that spotted owls once
nested in such habitats.
Many riparian ecosystems have deteriorated
in the Southwest (Cooperrider 1991, Bock et al.
1993, USDI 1994), and the loss of riparian
habitat was one of the reasons for listing the owl
(Part I). Dick-Peddie (1993) estimated from
map and air photo data that 96% of the Rio
Grande riparian area in New Mexico has been
lost to urbanization, agriculture, water impoundments,
and other modifications. Gallery forests
that once extended into woodlands, grasslands,
and deserts have significantly declined or deteriorated,
adversely affecting numerous wildlife
populations (Minckley and Clark 1984, Skovlin
1984, Minckley and Rinne 1985, Bock et al.
1993, USDI 1994). Efforts to improve riparian
and watershed conditions (DeBano and Schmidt
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Mexican Spotted Owl Recovery Plan
1989a, 1989b) could facilitate movements of
spotted owls between distant geographic locations
and perhaps even provide nesting habitat.
A wide variety of other organisms would also
benefit from healthier riparian systems.
TIMBER TIMBER TIMBER HARVEST HARVEST AND
AND
SILVICULTURAL SILVICULTURAL SILVICULTURAL PRACTICES
PRACTICES
Historically, the principal objectives of forest
management were to derive economic gain and
commodities from forests. Silviculture has great
potential as a tool for meeting other objectives,
however, such as maintaining and developing
Mexican spotted owl habitat, alleviating fire risk,
minimizing impacts of insects and disease, and
enhancing various ecological values. In this
section, we review past timber-harvest practices
in the Southwest and contrast those practices
with alternatives. Our focus is the potential
effects of these practices on Mexican spotted
owls.
Historical Historical Perspectives
Perspectives
Past Past Practices
Practices
The primary factors leading to the listing of
the Mexican spotted owl were adverse modification
of its habitat as the result of even-aged
management and plans to continue this harvest
method as detailed in existing Forest Plans.
Fletcher (1990) reported the loss of >325,000 ha
(800,000 acres) of spotted owl habitat within FS
Region 3 as the result of human activities,
primarily forest management. Silviculture
emphasized even-aged systems which tended to
simplify stand structure and harvest a disproportionate
share of large trees. The Team used past
forest inventory data to evaluate the change in
the size-class distribution of trees from the 1960s
to the 1980s. The trend that emerged from our
analysis was a substantial increase in the density
of trees 12.7-32.8 cm (5-12.9 in) dbh, but a
large decrease in numbers of trees >48.3 cm (19
in) dbh (see below). As discussed by Ganey and
Dick (1995), large trees are an important component
of spotted owl habitat; thus, the 20%
decrease in numbers of trees >48.3 cm (19 in)

dbh removed a key habitat component of the
Mexican spotted owl. The simplification of stand
structure is not so easily quantified. Given that
mostly even-aged management was used, however,
the conclusion of stand simplification is
reasonable.
Forest Forest Plans
Plans
Existing Forest Plans and their underlying
standards and guidelines are fairly explicit with
respect to the silvicultural practices to be used
and the expected timber volumes to be extracted.
These Forest Plans articulate classic even-aged
management regimes with regeneration treatments
occurring at 120-year intervals, intermediate
treatments employed to maintain open stand
conditions, and disease-control treatments as
conditions warrant. Thus, management called
for fairly frequent entries into a stand. Further,
this management system stressed simple stand
structures, decreased residual densities, and
elimination of large, slow-growing, but high
value trees (primarily ponderosa pine and Douglas-fir).
Salvage, sanitation, fuel reductions, and
fuelwood harvest as specified in Forest Plans
combined to reduce numbers of snags, another
correlate of spotted owl habitat. In summary,
even-aged management as specified in Forest
Plans is incompatible with maintaining and
developing spotted owl habitat. The Team is
encouraged, however, by recent efforts by FS
Region 3 to amend forest plans to incorporate
the recommendations proposed in this Recovery
Plan, and to emphasize uneven-aged management
as the preferred silvicultural system in the
Region.
Habitat Habitat Trends
Trends
Historical and current trends in spotted owl
habitat are presently unknown. Numerous
factors underlie this lack of knowledge, but the
paucity of reliable vegetation data is the most
glaring explanation. This lack of credible data
has not precluded rampant speculation on
habitat trend, however. In general, habitat trend
is perceived in two divergent ways. One view is
that past timber harvest within the forest types
used by Mexican spotted owls has caused a
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Mexican Spotted Owl Recovery Plan
dramatic decline in habitat quantity and quality.
Indeed, the conclusion of historical habitat loss
coupled with projections for additional habitat
loss were the primary factors for listing the
subspecies (Part I). The contrary view suggests
that many years of fire exclusion within Southwestern
forests has allowed mixed-conifer forest
types to increase at the expense of meadows and
fire-disclimax species such as quaking aspen and
ponderosa pine (USDA 1993b, Johnson 1994).
Further, Southwestern ponderosa pine forests are
known to be generally denser today than they
were in pre-settlement times (Covington and
Moore 1992, 1994a, b, c). Based on this information,
USDA (1993b) concluded that habitat
suitability for the Mexican spotted owl had
increased. Because of these conflicting views, the
Team attempted a quantitative evaluation of
habitat trend with respect to the Mexican spotted
owl.
Data Data Data Availability. Availability.—Limited Availability. sources of data are
available for assessing habitat trend. Within
forested types, forest inventories from the 1960s
(Choate 1966, Spencer 1966) and the 1980s
(Conner et al. 1990, Van Hooser et al. 1993)
have been compared by USDA (1993b) and
Johnson (1994) and are used, in part, for our
analyses. We admit, however, that differences in
definitions and in how data were collected make
comparisons between the 1960s and 1980s data
tenuous, at best (Van Hooser et al. 1993). These
differences include: (1) changes in definitions of
vegetation types; (2) changes in the landbase
being sampled, (e.g., changes in wilderness
designation); and (3) changes in sampling
intensity.
The following comparisons are limited to
commercial forest lands within the States of
Arizona and New Mexico on a per hectare basis.
Thus, all forest types are included but, unlike
USDA (1993b) and Johnson (1994) we do not
extrapolate the data to unsampled forested lands
such as wilderness areas. Therefore, our analyses
focus on changes on commercial forest lands
where data exist. Because of differences in land
designations (i.e., commercial timber land
becoming wilderness between the two sampling
periods), comparisons of raw values are potentially
misleading. Thus, our comparisons are

primarily restricted to evaluations of proportions.
To compare stand structure, we used
relative frequencies of trees by size class. We
reiterate that caution is warranted when inferring
conclusions from these data, but submit that
some gross generalizations are possible.
Trends Trends in in Forest Forest Landbase Landbase and and Timber
Timber
Volume.— Volume.—Total Volume.— forested land increased from
4,516,000 to 4,750,000 ha (11,160,000 to
11,738,000 acres) from the 1960s to the 1980s,
roughly a 5% increase. The commercial forest
landbase decreased by approximately 15%
(624,000 ha [1,541,000 acres]), however, and
reserved forested lands increased by 858,000 ha
(2,119,000 acres). Growing stock (i.e., the
harvestable volume) on commercial lands decreased
from 12,707 MMCF to 11,549 MMCF.
This decrease is not surprising given the volume
of timber harvested on commercial forest lands
and the decrease in the amount of commercial
forest lands from the 1960s to the 1980s.
Trends Trends in in in Forest Forest Types. Types.—Within Types. the commercial
landbase, mixed-conifer forests comprised
approximately 11% of total area in the 1960s
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Mexican Spotted Owl Recovery Plan
Table able II.D.1. II.D.1. Changes in the area (ha X 1,000 [acres x 1,000]) and distribution of forest types from
the 1960s to 1980s on commercial forest lands within Arizona and New Mexico. Data from Choate
(1966), Spencer (1966), Conner et al. (1990), Van Hooser et al. (1993).
__________________________________________________________________________________________
__________________________________________________________________________________________
Landbase Landbase Propor opor oportion opor tion of of Landbase Landbase Propor opor oportion opor tion of of Change Change in
in
For or orest orest
est Type ype ype in in 1960s 1960sa
1960s 1960s 1960s Landbase Landbaseb
in in 1980s 1980s 1980sa
1980s 1980s Landbase Landbaseb
P PPropor
P opor oportion opor tion c
__________________________________________________________________________________________
__________________________________________________________________________________________
Ponderosa Pine 3,234 78 2,530 72 -6
[7,992] [6,252]
Mixed-conifer 475 11 709 20 9
[1,173] [1,752]
Spruce-fir 257 6 201 6 0
[635] [496]
Quaking aspen 180 4 81 2 -2
[446] [201]
Total otal 4,146 4,146 100 100 3,523 3,523
100
100
[10,246] [10,246] [10,246]
[8,701] [8,701]
[8,701]
__________________________________________________________________________________________
a Landbase in hectares [acres] covered by the forest type.
b Proportion of the total forested landbase belonging to the forest type.
c (Prop. 1960s landscape)-(Prop. 1980s landscape).
67
and 20% of the total area in the 1980s, a 9%
increase (Table II.D.1). Possible explanations for
this change include: (1) increasing invasion of
mixed-conifer species (presumably Douglas-fir
and white fir) into other types, such as meadows;
(2) more liberal definitions of mixedconifer
(i.e., includes types previously classified
as something else); (3) quaking aspen giving way
to other species in the absence of fire; and (4)
selective harvest of ponderosa pine, leaving
residual forests composed primarily of other
conifer species. Any of these reasons may explain
the perceived changes of forest type; probably all
of these and other factors contributed to some
degree. We speculate that classification changes
account for most of the change, and that selective
removal of ponderosa pine and the succession
of quaking aspen stands to mixed-conifer
are also plausible short-term explanations.
Conversely, we have difficulty accepting that
encroachment of mixed-conifer species into
other forested types was responsible for more
than a relatively small portion of this change
within the twenty-year period. Thus, any generalizations
concerning changes in forest types and
any actions proposed to reverse these trends

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Mexican Spotted Owl Recovery Plan
Table able II.D.2. II.D.2. Changes in the density (trees/ha [trees/acre]) and distribution of tree size classes from
the 1960s to 1980s on commercial forest lands within Arizona and New Mexico. Data from Choate
(1966), Spencer (1966), Conner et al. (1990), Van Hooser et al. (1993).
Tree ee Density ensity Propor opor oportion opor tion of of Density ensity Propor opor oportion opor tion of of Change Change in in Density ensity
Siz iz ize iz e Class Class Class in in in 1960s 1960s 1960sa
1960s 1960s Total otal b in in 1980s 1980sa
1980 1980 Total otal b Propor opor oportion opor tion c Change
Change
Change d
2.5-12.5 cm 146.2 62.5 134.2 53.7 -8.8 -8.3
[1.0-4.9 in] [59.2] [54.3]
12.6-32.8 cm 70.3 30.0 98.5 39.4 9.4 40.2
[5.0-12.9 in] [28.5] [39.9]
32.9-48.0 cm 12.1 5.2 13.0 5.2 0.0 7.5
[13.0-18.9 in] [4.9] [5.3]
>48 cm 5.4 2.3 4.3 1.7 -0.6 -20.4
[>19 in] [2.2] [1.7]
a Tree density in no./ha [no./acre]
b Proportion of the total number of trees within that size class.
c (Prop. 1960s total)-(Prop. 1980s total).
d
([Prop. 1960s total]-[Prop. 1980s total])/(Prop. 1960s total).
must acknowledge this uncertainty, and should
consider all plausible explanations for these
trends.
Trends Trends in in Size-class Size-class Size-class Distributions.
Distributions.—We Distributions. noted
a change in the size-class distribution of trees on
commercial forest lands of Arizona and New
Mexico (Table II.D.2). Sapling-sized trees (2.5-
12.5 cm [1-4.9 in] dbh) decreased in both
absolute density and in relative contribution to
the size-class distribution; trees 12.6-31 cm
(5-12 in) dbh increased in density by 40% and
in relative proportion of the size class distribution
by >9%; and trees in the 31-48 cm (13-19
in) size class increased in density but not in
relative proportion of the tree distribution.
Finally, the density of large trees (>48 cm [19 in]
dbh) decreased from 2.3 to 1.7 trees/ha (0.9 to
0.7 trees/ac), a 20% decline. This decrease in
large trees would be expected given past timber
harvest practices which emphasized harvest of
the large trees. Possible explanations for the
increase in smaller stems include the growth of
regeneration, limited pre-commercial thinning,
fire suppression, and the lack of interest by the
forest industry in the smaller-sized stems.
Summary Summary Summary of of of Recent Recent Recent Habitat Habitat Habitat Trends. Trends. Trends.—Our
Trends. Trends.
analyses indicate that between the 1960s and
68
1980s (1) total forested acres increased, (2)
mixed-conifer types apparently covered more of
the landbase (but see above cautions regarding
this conclusion), and (3) densities of large trees
declined. Although the amount of total forested
land has increased and the amount of mixedconifer
forest may have increased, we doubt that
the amount of Mexican spotted owl habitat has
increased concomitantly. Given the 20-yr period
between inventories, most of these additional
acres are likely in early successional stages and
unlikely to possess the habitat characteristics
used by spotted owls. Conversely, the 20%
decrease in the density of large trees is an alarming
negative trend with respect to a very critical
component of spotted owl habitat.
Silvicultural Silvicultural Practices
Practices
and and Forest Forest Forest Management
Management
Four common forest structures occur naturally
or by silvicultural efforts. These structures
are even-aged, balanced uneven-aged, irregular
uneven-aged, and even-aged/uneven-aged
stratified mixtures. Even-aged stands, for the
most part, are characterized by most trees being
approximately the same age. The general convention
is that the spread of ages within the
stand are within approximately 20% of the

specified rotation age. Two types of uneven-aged
stands are balanced and irregular stands. In both
cases, at least three distinct age classes exist. A
balanced uneven-aged stand equates to each age
class occupying roughly equal areas. Distribution
by diameter class approximates a reverse, jshaped
curve. Irregular uneven-aged stands have
some age and associated diameter classes missing
across the possible range of ages and diameters.
A two-storied stand, one with two distinct ageclass
and diameter distributions, is neither evenor
uneven-aged, but is intermediate between the
two. Stratified mixtures occur where trees are
essentially even-aged, but differences in growth
rates and shade tolerance among tree species
result in multiple canopy strata. This structure
also occurs when selective regeneration of shadetolerant
species or high site productivity leads to
heterogeneous age and diameter distributions.
In much of the mixed-conifer type in the Southwest,
the stratified-mixture of stand structure
appears to be relevant to habitats used by spotted
owls.
Silviculture
Silviculture
Silviculture has been variously defined as (1)
the art of producing and tending a forest, (2) the
application of knowledge of silvics in the treatment
of a forest, and (3) the theory and practice
of controlling forest establishment, composition,
structure and growth (Smith 1986). In a general
sense, silviculture is the practice of managing
forest establishment, composition, structure, and
growth to meet stated objectives. Thus, silviculture
should be regarded as a system of treatments
and not solely the practice of removing trees
from a stand.
In the Southwest, two broad classifications
of silvicultural systems, based on methods of
reproduction and resulting age-class mixes of
forested stands, are even-aged and uneven-aged
management. These are reviewed below; again,
our focus is the potential these systems have for
developing spotted owl habitat.
Even-aged Even-aged Management.
Management.—Even-aged Management.
management
has been used commonly in Southwestern
forests. Reasons for its popularity are based both
on ecology and economics. Ecologically, even-
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Mexican Spotted Owl Recovery Plan
aged systems favor species with limited shade
tolerance, such as quaking aspen, oaks, and
lodgepole pine. Shade tolerance is the ability to
reproduce and grow under the shade of larger,
taller trees. Shade-tolerant species typically
include true firs in Southwestern forests. Ponderosa
pine is considered to be of intermediate
shade tolerance, but tending toward the intolerant
side. Economically, even-aged management
is more efficient when considering short-term
costs of site utilization, sale preparation, transportation
systems, harvesting, and slash reduction.
Further, even-aged systems are easier to
model, administer, and track over time.
Regeneration methods within even-aged
systems of the Southwest include shelterwood,
clearcutting, and seed tree methods. The
shelterwood method typically has a series of
cuttings. The first treatment in mature stands is
to stimulate cone and seed production for
regeneration. This is followed by a series of
treatments that remove the larger, older stems as
regeneration matures. Variations on the general
method include irregular shelterwood and
group-shelterwood. Clearcutting involves the
removal of the entire stand in one cutting.
Reproduction is obtained artificially by seeding
or planting, or naturally by seeding from adjacent
stands. This method is appropriate for
shade-intolerant species. In appearance,
clearcutting is indistinguishable from the coppice-forest
method of regeneration for quaking
aspen, where reproduction is obtained from
suckering of sub-terrain clones. The seed-tree
method resembles clearcutting except that a few
trees are left to provide a source of seed within
the treated area. Of these three, the shelterwood
method is used most commonly in the Southwest;
clearcut and seed-tree methods are used
infrequently.
Variations of even-aged management are
used throughout the Southwest, but all share the
following characteristics. A predetermined time
for regeneration of the stand is set a priori; this
regeneration time can vary. The FS Region 3
generally schedules regeneration treatments from
100 to 120 years of stand age, an age when trees
are expected to reach 45.7 cm (18 in) dbh as the
maximum size. The management objective is to
maximize total volume over time while provid-

ing a “saw-timber” sized product. Residual stand
density can be controlled by thinning at theoretically
scheduled entries in the stand. This
enables the capture of mortality on a semiregular
basis and provides intermediate revenues
from timber harvest.
Even-aged stand structures are not used to
any great extent by the Mexican spotted owl.
Further, with its intent to promote uniformity in
tree age, size, spacing, and density, even-aged
management generally would not be a preferred
system for short-term development of spotted
owl habitat. Even-aged management may be
appropriate to maintain quaking aspen within
the mixed-conifer type, however. Quaking aspen
is typically even-aged in its earlier stages of stand
development. Because of its extreme shade
intolerance and requirements for elevated soil
temperatures for sprouting, quaking aspen
should be managed under even-aged systems.
Later seral stages of quaking aspen that include a
mixed-conifer understory appear both as a
simple mixture of an even-aged overstory and
uneven-aged understory, or as a stratified mixture.
As decadent quaking aspen stands are
replaced by the shade-tolerant conifers, spotted
owl nesting/roosting habitat begins to develop.
In summary, even-aged management has limited
potential with respect to developing the types of
stand structures used by spotted owls. Nevertheless,
even-aged management is a critical tool to
meet specific objectives, and can meet certain
ecosystem objectives if employed at the proper
scale. Perhaps the primary objection to its use in
the past was its uniform, widescale application
across the Southwest.
Uneven-aged Uneven-aged Management.
Management.—Uneven-aged
Management.
management entails the removal of timber in all
size classes on a periodic basis so that regeneration
is continuously established over time, and
stand size-class distribution is regulated. Uneven-aged
management is loosely based on the
premise that density control across a range of
diameter classes will ensure growth of stems over
time to a set maximum diameter, while ensuring
regeneration of species at regular intervals over
time. Only one reproduction method, the
selection method, is used with uneven-aged
management. The selection method provides
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Mexican Spotted Owl Recovery Plan
openings in the stand to enable regeneration to
occur. Simultaneous with the selection and
harvest of trees to provide growing space for
regeneration, trees across all diameter classes are
thinned to ensure the desired distribution of
size- and age-classes within the stand.
Two variations of the selection method are
individual tree selection and group selection.
Individual tree selection, as the name implies,
involves the removal of single, scattered trees.
This method generally favors shade-tolerant
species, but this is also a function of the residual
stocking levels. Group selection entails the
removal of a small patch of trees; the width of
the patch is usually less than twice the height of
the dominant (i.e., largest) tree. This is somewhat
analogous to a very small clearcut, but the
difference between the group selection and the
clearcut method is in the spatial scale of application.
Group selection is used to create a balance
of age- or size-classes in small contiguous groups
resulting in a mosaic within a stand. In contrast,
even-aged methods are typically applied to an
entire stand. Group selection can be used to
promote the establishment and growth of shadeintolerant
trees since there is opportunity to
reduce localized residual densities and the
amount of area shaded.
Group selection offers a number of advantages
for the development of potential spotted
habitat over single-tree selection techniques.
Application of the group selection method could
provide a mosaic of many small even-aged or
two-storied groups across a forest stand. Regeneration
of shade-intolerant species is possible
where a reproduction source, either clones or
seeds, is present. With respect to insect and
disease problems, management options increase
for both suppression and prevention, especially
in mixed-species stands. Edge effects found at
group interfaces can provide structural features
and openings that mimic gap-phase regeneration,
and provide early-seral vegetation for prey
species (Ward and Block 1995). In some cases,
group-selection methods may result in less
residual damage to the stand as the result of
logging activities than single-tree selection.
Uneven-aged silvicultural practices predominate
on Tribal lands where commercial timber
harvest exists. Reasons for the emphasis on this

silvicultural system include aesthetics, providing
forest cover over all lands simultaneously, the
perception that it provides a more even-flow of
products than even-aged management, and the
fact that it allows continuous regeneration.
We have not been able to assess the effects of
classic uneven-aged management on Mexican
spotted owl habitat because we were unable to
acquire data for most areas where uneven-aged
management is practiced on a large scale. However,
based upon our understanding of the
application of uneven-aged systems, stand
density is often kept at a fairly low level, seldom
exceeding 18 m 2 /ha (80 ft 2 /acre) of basal area.
These low residual stand densities allow for
regeneration and growth of ponderosa pine.
Uneven-aged systems, whether they retain
individual trees or groups of trees, allow for the
development of multiple canopy levels, a key
component of Mexican spotted owl habitat.
However, Ganey and Dick (1995) demonstrate
clearly that owl habitat typically also includes
significant numbers of large trees. These large
trees may not be retained where uneven-aged
management is applied in this fashion.
In summary, uneven-aged management has
some promise for providing stands exhibiting
characteristics of spotted owl habitat. As currently
practiced, however, uneven-aged management
results in large acreages of low-density
stands, numerous road openings, and the eventual
eradication of large diameter stems. Although
neither the short- or the long-term
effects of these applications on spotted owls are
known, this type of application may not be the
best option for producing spotted owl habitat.
Development Development or or or maintenance maintenance of of stratified
stratified
mixtures. mixtures. mixtures.—Stratified mixtures. mixtures can originate in
various ways, including stand-replacing events
(e.g., crown fire, even-aged management) that
may or may not leave remnant stems. The
establishment of stratified mixtures is not likely
in mixed-conifer types within the short time
frame (10-15 years) of this Recovery Plan.
Maintenance of such stands could be considered
in the short-term, however, and development of
stratified mixtures could be incorporated in
longer-term management plans.
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71
Mexican Spotted Owl Recovery Plan
Management for stratified mixtures must
consider the mix of species along the continuum
of shade tolerance. Thus, any regeneration
efforts should be designed to have enough
openings of sufficient size for seedling/sprouting
establishment and release. Openings can be
accomplished by group selection cuts favoring
retention of shade-intolerant species, or selection
of individual trees adjacent to stems that could
provide a seed source for regeneration. One
technique to consider is small-scale seed tree cuts
(perhaps to be thought of as group seed-tree
selection cuts), which would provide both a seed
source and trees for ultimate snag development.
This method could maintain shade-intolerant
species, but would not be intrusive enough to
produce even-aged structure throughout the
stand. Within stratified mixtures, intermediate
treatments including pre-commercial and
commercial thinning could be beneficial in
increasing the growth of residual trees. At some
point, however, further treatments should be
deferred, and natural stand maturation and
succession should be allowed to proceed until
either (1) the stand is no longer spotted owl
habitat; or (2) the stand can be replaced by
habitat (preferably occupied by spotted owls)
that has been developed elsewhere.
Conclusions
Conclusions
Clearly, recent forest management practices
and those detailed in existing Forest Plans are
not beneficial to Mexican spotted owls. Reliance
on traditional forest management and silvicultural
techniques may no longer be possible, not
only with respect to the conservation of the
Mexican spotted owl but also with respect to
maintaining other ecosystem attributes. New
approaches must be developed that ensure the
long-term provision of owl habitat and the
maintenance of ecosystem structure and function.
Traditional approaches will still have their
role, but perhaps used in slightly different ways
and with different intensities. Innovative applications
of uneven-aged management may be
particularly useful in developing and maintaining
spotted owl habitat. In addition, particular
applications of uneven-aged management may
be useful in maintaining habitat conditions for

the owl where they exist. In some cases, the
application of even-aged management systems
may also be appropriate, so future forest management
should not preclude the use of evenaged
management.
Volume I/Part II
GRAZING
GRAZING
Grazing by livestock and wildlife (e.g., elk,
deer) occurs throughout the range of the Mexican
spotted owl. Depending on the intensity,
grazing has the potential to influence habitat
composition and structure, and affect food
availability and diversity for the owl. However,
predicting the magnitude of grazing effects on
spotted owls and their habitat, and evaluating
management options requires a better understanding
of the relationship between spotted owl
habitat and grazing.
Specific studies that document the effects of
livestock and wildlife grazing on spotted owl
habitat have not been conducted. Until specific
information is available, the potential effects on
the owl of grazing and trampling of vegetation
must be identified and considered to the extent
possible. For example, livestock and wildlife may
not impact spotted owl roost and nest sites
immediately, but could alter riparian habitats by
reducing, eliminating, or suppressing regeneration.
In time, reduced regeneration could limit
the development of overstory structure needed
for nesting, roosting, and other life history
needs, as well as jeopardize the sustainability of
these habitat types.
Grazing can alter a plant community directly,
indirectly, or both. Direct alterations may
be as obvious as plant removal by consumption
or as subtle as removal by trampling. Indirect
alterations may be as straightforward as loss of
seed source or as insidious as damaged soil
(Dwyer et al. 1984, Kauffman and Krueger
1984, Fleischner 1994). Moderate to heavy
grazing can reduce plant density, cover, biomass,
vigor, and regeneration ability. Collectively, these
factors can alter the relative composition and
structure of grass, forb, shrub, and tree components
in an area (Hanley and Page 1982,
Zimmerman and Neuenschwander 1984, Schulz
and Leininger 1990, Milchunas and Lauenroth
1993). Within conifer forests, grazing can
72
Mexican Spotted Owl Recovery Plan
remove or greatly reduce grasses and forbs,
thereby allowing large numbers of conifer
seedlings to become established because of
reduced competition for water and nutrients and
reduced allelopathy. Establishment of large
numbers of seedlings coupled with the reduction
in light ground fuels (i.e., grasses and forbs) may
act synergistically with fire suppression to
contribute to dense overstocking of ladder fuels.
This dense overstocking can alter forest structure
and composition and degrade spotted owl and
prey habitats while increasing risks of standreplacing
fires.
Beyond the effects of grazing on plants,
livestock activity can increase duff layers, accelerate
decomposition of woody material, produce
compacted soils, damage stream banks and
channels, and damage lake shores (Kennedy
1977, Blackburn 1984, Kauffman and Krueger
1984, Skovlin 1984, Clary and Webster 1989).
The combination of these changes to the biotic
and physical landscapes also affects plant community
composition, structure, and vigor. If
such changes occur in or near areas used by
spotted owls, then grazing can influence the owl.
Those influences can be manifested by altering
(1) prey availability, (2) susceptibility of spotted
owl habitat to fire, (3) the health and condition
of riparian communities; and (4) development of
habitat. We summarize below the major suspected
influences of grazing on Mexican spotted
owls.
1. For the Mexican spotted owl, prey
availability is determined by the distribution,
abundance, and diversity of prey
and by the owl’s ability to capture it.
Grazing may influence prey availability
in dissimilar ways. For example, grazing
that reduces dense grass cover can create
favorable habitat conditions for deer
mice while creating unfavorable conditions
for voles, meadow jumping mice,
and shrews (Medin and Clary 1990,
Schultz and Leininger 1991). This
change might decrease prey diversity
(Medin and Clary 1990, Hobbs and
Huenneke 1992). A diverse prey base can
provide a more predictable food resource
for the owls over time, because popula-

Volume I/Part II
tions of many small mammals fluctuate
asynchronously. Conversely, short-term
removal of grass and shrub cover may
improve conditions for the owl to detect
and capture prey. Long-term loss of
grasses, forbs, and shrubs may promote
tree growth and cover that could decrease
prey abundance. Thus, grazing can pose
ecological tradeoffs.
2. Grazing that significantly reduces herbaceous
ground cover and increases shrubs
and small trees can decrease the potential
for beneficial low-intensity ground fires
while increasing the potential for
destructive high-intensity vertical fires
(Zimmerman and Neuenschwander
1984). Low-intensity ground fires
prevent fuel accumulation, stimulate
nutrient cycling, promote grasses and
forbs, discourage shrubs and trees, and
perpetuate the patchiness that supports
small mammal diversity. Catastrophic
fire reduces or eliminates foraging,
wintering, dispersal, roosting, and
nesting habitat components.
3. Excessive grazing in riparian areas can
reduce or eliminate important shrub,
tree, forb, and grass cover, all of which in
some capacity support the owl or its
prey. Excessive grazing can also physically
damage stream channels and banks
(Ames 1977, Kennedy 1977, Kauffman
et al. 1983, Blackburn 1984, Slovkin
1984, Clary and Webster 1989, Platts
1990.) Deterioration of riparian vegetation
structure can allow channel widening.
This event, in turn, elevates water
and soil temperatures and thus evaporation
and lowering of water tables, plus it
significantly increases the potential for
accelerated flood damage (Platts 1990).
These processes alter the microclimate
and vegetative development of riparian
areas, potentially impairing its use by
spotted owls.
4. Excessive grazing, sustained for long
periods, can inhibit or retard an area’s
73
Mexican Spotted Owl Recovery Plan
ability to produce or eventually mature
into habitat for the owl or its prey. This
will probably prove to be an inevitable
consequence of the events and processes
described above.
The potential for grazing to influence
various components of spotted owl habitat
cannot be ignored. However, current predictions
of grazing effects on plant communities as they
relate to the owl are inexact. Thus, the integration
of spotted owl needs and grazing management
will require coordination, and an interactive
and adaptive approach between protection,
restoration, and management.
RECREATION
RECREATION
Recreational activities may affect Mexican
spotted owls directly by disturbing nests, roosts,
or foraging sites. Disturbance may occur indirectly
through altered habitat caused by trampling
of vegetation, soil damage, or both. Developing
new recreation facilities or expanding
existing facilities, such as campgrounds and
trails, may alter spotted owl habitat and habitat
use and perpetuate disturbance impacts caused
by recreation.
If a given recreational activity does not cause
habitat alteration, the Team assumes that that
activity generally has relatively low impact
potential with respect to spotted owls. However,
exceptions may exist in local situations or certain
RUs where the level of recreational activities is
high. Essentially, the determining factor of an
activity’s impact on spotted owls is a combination
of its location, intensity, frequency, and
duration rather than simply its character.
Types Types of of Recreation
Recreation
Recreational activities fall into several categories;
the number, size, and intensity of such
activities will vary with location. The following
general categories include most widespread
recreational activities that might affect spotted
owls and their habitat.

Camping Camping
Camping
Although the effects of camping on spotted
owls have not been studied, disruption of nesting,
roosting, and foraging activities is a distinct
possibility. The character of camping varies
dramatically, however. One person may camp
alone in a small tent, whereas others may camp
in groups with motorhomes. The disparity in
character does not necessarily translate to disturbance
potential, however. One person camping
in a nest grove could be more disruptive than 12
people camping in a foraging area. Therefore,
blanket generalizations about the impacts of
camping activities are inappropriate. These
activities should be assessed on a case-by-case
basis, considering factors such as the location of
the activity relative to the owls, the number of
individuals involved, the type of group involved,
and the frequency and duration of the activity.
Hiking
Hiking
Hiking is typically a short-term activity, and
may bring a person into and out of an owl’s
presence relatively quickly. Most spotted owls
appear to be relatively undisturbed by small
groups (

Volume I/Part II
SUMMARY
SUMMARY
Part III of this Recovery Plan outlines
management guidelines to alleviate threats to the
spotted owl. These recommendations are based
largely upon the Team’s evaluation of the biology
of the owl as detailed in Volume II. From these
analyses, the Team has drawn the following
conclusions.
Mexican spotted owls generally occupy
remnants of the landscape that have experienced
minimal human disturbance. We acknowledge
that exceptions to this generalization occur.
These remnants include inaccessible canyons,
steep slopes, wilderness, and other environments
not heavily modified by humans. Persistence of
owls depends partly on these remnant patches,
but these environments alone may be insufficient
to ensure long-term conservation of the
Mexican spotted owl. A key point here is that
not all human activies are detrimental to spotted
owls. In fact, if directed appropriately, some
human activities can be used to the owl’s benefit.
Consequently, management must focus on
75
Mexican Spotted Owl Recovery Plan
creating new habitat to replace remnants that
become no longer appropriate for the owl.
Creation of replacement habitat hinges on
understanding patterns of natural variation and
modifying human activities that might conflict
with the development of habitat. Natural variation
across the landscape results from unique
biophysical conditions at each location on the
land. Further, effects of human activities are
equally variable across the landscape. Although
we cannot ascribe strict cause-effect relationships
of natural processes and human activities on
Mexican spotted owls, we can draw certain
inferences about their probable impacts. The
previous section detailing the conceptual framework
underlying the recovery measures provides
the rationale for those inferences. Thus, the
management recommendations (Part III) were
based on two interrelated sets of information: (1)
basic knowledge of Mexican spotted biology;
and (2) understanding how various natural
processes and human activities modify the
environment to maintain, develop, and alter
spotted owl habitat.

Recovery
Volume I, Part III

Removing a species or subspecies from
threatened status becomes a primary management
objective the moment listing is finalized.
Listing a species as threatened affords more
protection to the species than it would normally
receive through other laws governing wildlife.
Specifically, “threatened” status implies that
human activities and/or natural disturbances
pose greater than normal risks to the entire
species or subspecies rather than just to individuals.
Greater protection can manifest itself as
more explicit and careful regulation of human
activities. In some measure, a Recovery Plan
reconciles human needs and desires with the
survival needs of the threatened species or
subspecies. If successful, the reconciliation
process leads to an arrangement to accommodate
both people and the threatened species. Ultimately,
careful regulation of human activities
combines with careful management of natural
resources to allow removing the species from
threatened status, or “delisting.” Just as listing a
species requires a process of information gathering
and assessment, delisting requires a similar
process.
THE THE DELISTING DELISTING PROCESS
PROCESS
Section 4 of the Act governs the listing,
delisting, and reclassification of species, the
designation of critical habitat, and recovery
planning. Regulations implementing listing,
delisting, reclassification, and critical habitat
designation are codified at 50 CFR 424.
The process of delisting a species or subspecies
is essentially the same as that of listing: a
proposed rule describing the justification for the
action is published in the Federal Register; a
public comment period is opened, including
public hearings if requested; and, within one
year of the proposal, either a final rule delisting
the species or a notice withdrawing the proposed
rule is published in the Federal Register.
In considering whether to delist a species,
the same five factors considered in the listing
process (see Part I) are evaluated. While emphasis
may be given to those factors leading to the
Volume I/Part III
A. A. DELISTING
DELISTING
76
Mexican Spotted Owl Recovery Plan
species’ listing, all of the factors must be evaluated
in making a delisting determination.
Section 4(c)(2) of the Act directs the FWS to
conduct, at least once every five years, a review
of all listed species and determine for each
species whether it should be removed from the
list, reclassified from endangered to threatened,
threatened to endangered, or remain in its
current status. This Recovery Plan lists criteria
only for delisting the Mexican spotted owl. Any
decision to reclassify the subspecies to endangered
status will be made by the FWS either as a
result of the aforementioned mandatory review
or at any other time information becomes
available indicating that reclassification is appropriate.
Section 4(g) of the Act directs the FWS to
implement a system in cooperation with the
States to monitor effectively for not less than five
years the status of a species or subspecies that has
been delisted due to recovery. The provisions of
the Act do not apply to the delisted species
during this monitoring period. However, the
FWS could relist a species, through the standard
listing process, should monitoring indicate that
the species will decline without the Act’s protection.
DELISTING DELISTING CRITERIA
CRITERIA
We recognize that we lack data and authority
to prescribe and implement monitoring strategies
for Mexico. Thus, our recommendations
below apply only to the U.S. range of the
Mexican spotted owl. We recommend that
Mexican authorities develop similar delisting
criteria and monitoring schemes for delisting in
Mexico.
Five specific criteria must be met before the
Mexican spotted owl can be delisted in the U.S.
The first three criteria, which operate at a
multiple-RU level, must be satisfied before the
last two criteria, which operate at the RU level,
apply. These are the three overriding criteria:
1. The populations in the Upper Gila
Mountains, Basin and Range - East, and

Volume I/Part III
Basin and Range - West RUs must be
shown to be stable or increasing after 10
years of monitoring, using a study design
with a power of 90% to detect a 20%
decline with a Type I error rate (a) of
0.05.
2. Scientifically-valid habitat monitoring
protocols are designed and implemented
to verify that (a) gross changes in
macrohabitat quantity across the U.S.
range of the Mexican spotted owl are
stable or increasing, and (b) microhabitat
modifications and trajectories within
treated stands meet the intent of the
Recovery Plan.
3. A long-term, U.S.-rangewide management
plan is in place to ensure appropriate
management of the subspecies and
adequate regulation of human activity
over time.
Once these three criteria are satisfactorily
achieved, delisting may occur in any U.S. RU
that meets the final two criteria:
4. Threats to the Mexican spotted owl
within the RU are sufficiently moderated
and/or regulated.
5. Habitat of a quality to sustain persistent
Mexican spotted owl populations is
stable or increasing within the RU.
These criteria are, by design, redundant and
dependent. Meeting one criterion, to some
degree, requires meeting all or some portion of
the other criteria. Integrating the criteria is
unavoidable but nevertheless desirable. Progress
on one translates to progress on all.
Monitoring Monitoring Population Population Trends
Trends
For a statistically valid monitoring design, we
suggest the quadrat sampling scheme described
in III.C. The three RUs where population
monitoring is required for delisting represent the
bulk of the known Mexican spotted owl population
in the U.S. No population delisting criteria
77
Mexican Spotted Owl Recovery Plan
are applied to the remaining U.S. RUs because
they would be difficult to monitor because of
the small, fragmented nature of the populations.
A premise for our population monitoring
approach is that the existing Mexican spotted owl
population in the U.S. is adequate. This premise
will be tested by monitoring population trends.
If the results of monitoring indicate that the
U.S. population is stable or increasing over the
next 10 to 15 years (assuming 10 years prior to
delisting followed by the required 5 years after
delisting), the Team is willing to accept that the
current population will remain viable in the
foreseeable future and to assume that the population
is recovered. That is, the Team believes that
if the current population is able to maintain
itself, or to increase, then the population has
exhibited evidence that it is of ample size to
persist.
Our basis for the parameters included in the
delisting criteria are as follows. The annual rate
of change of the population within a RU can be
estimated as l = N /N . A population is stable if
t+1 t
l = 1, decreasing if l < 1, and increasing if
l > 1. A 20% reduction over a 10-year period
implies a value of l = 0.978; i.e., l10 = 0.80.
To conclude that a population is stable, we
fail to reject the null hypothesis that l = 1, or
alternatively, that the 95% confidence interval
on l includes 1. If we fail to reject this null
hypothesis, we want to ensure that the possible
rate of decline is very small. Thus, we suggest a
Type II error rate of 0.10, and for a 15-year
period, the annual estimate of l is
0.98523 = 0.8 (1/15) ^ ^ ^
.
For this statistical test of trend, continued
persistence of the Mexican spotted owl population
means the Type II error rate is more important
than the Type I error rate. That is, a Type I
error means that we mistakenly conclude that
the population is declining when it is not.
Although costly measures might be taken to
reverse our incorrect perception of the trend in
the owl population, the persistence of the
population is not threatened. In contrast, a Type
II error means that we conclude the population
is stable or increasing when it is really declining.
Thus, persistence of the population could be in
jeopardy because measures would not be taken
to correct the decline. Therefore, we emphasize

that a low Type II error rate of b = 0.10 (power
is 1 - b = 0.90) must be met to delist the species.
Several biological reasons lead us to select a
time span of 10-15 years for monitoring. The
mean life span (MLS) of Mexican spotted owls
that reach adulthood falls within this range.
MLS is calculated as 1/(-log(S)), with S representing
the adult survival rate. Using S = 0.8889
(SE = 0.0269), survival rates calculated from the
demographic study areas, the MLS is about 8.5
years. Calculating confidence intervals for MLS
yields 16.6 years as an upper age limit. Population
turnover rates provide another biological
argument for the time span (x) required for
delisting. For example, we can estimate the time
that it takes 90% of the youngest members of
the adult population to completely turn over, or
for 90% of the existing young adult birds to die.
Given the adult S of 0.8889, solving for x in
0.8889 x = 1 - 0.90 gives x = 19.6 years for 90%
of a given cohort of young birds to turnover. A
50% turnover would be 5.9 years, which would
correspond to the median life span. For x equals
10 years, 70% of the young adult population
will have turned over.
The time duration for the monitoring and
magnitude of change required to detect a population
decline are related. Thomas (1990) argued
that the minimum viable population size depended
on the temporal variation expected in a
population. Species with much temporal variation
in their population size might normally
exhibit a 20% decline over a short period. We do
not expect Mexican spotted owl populations to
display much temporal variation. The most
variable aspect of their population biology is
probably recruitment, and years of little or no
recruitment may occur. However, because of the
high adult survival rate, the decline in the
population during a year of no recruitment
would still only be 11%. Thus, two consecutive
years of no recruitment would result in a 21%
decline. But the fecundity estimates presented by
White et al. (1995) suggest that no recruitment
is unlikely. Thus, we conclude that a 20%
decline over a 10-year period indicates the
population is truly declining and is not the result
of normal temporal variation.
The choice of a Type II error rate of 0.10 is
somewhat arbitrary. However, this value interacts
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Mexican Spotted Owl Recovery Plan
with the choice of a 20% decline over the 10year
period. Figure III.A.1 depicts a hypothetical
curve for power as a function of the size of the
effect being detected (labeled Detectable Effect
Size in the graph). We could specify that a 15%
change is detectable with a 67% power, or that a
25% change is detectable with a 94% power.
These statements are all equivalent in terms of
the effort required for the monitoring protocol
(as shown by the graph). This is because the
relationship between the detectable difference
and the power to detect this difference is fixed
by the monitoring effort (normally considered as
the sample size of the statistical procedure).
Thus, we have suggested that a 90% power to
detect a 20% decline over 10 years is a reasonable
point to fix the function that relates power
and magnitude of the detectable effect.
In summary, we believe 10 years is a reasonable
time span for monitoring because more
than half of the adult population has turned
over. Further, we expect that the population
would have been subjected to adequate environmental
variation during this 10-year period.
Once the species is delisted, the additional five
years of monitoring as required under the Act
Figure Figure Figure III.A.1. III.A.1. Hypothetical curve of the
statistical power to detect a trend in a population.

should provide further assurance that the population
is not declining.
We believe that the delisting criterion
proposed here provides positive incentives to
land-management organizations to vigorously
pursue the proposed population monitoring
system. Delisting of the species depends on
providing clearly specified evidence that the
population is stable or increasing. The sooner
the responsible land-management organizations
begin the population monitoring, the sooner the
owl can be delisted.
Other Other Other Considerations Considerations of of Population
Population
Monitoring
Monitoring
The proposed procedure for population
monitoring only monitors the territorial population
of owls. Because nonterritorial owls (“floaters”)
do not respond to the usual methods of
locating them (i.e., calling), the only method of
monitoring nonterritorial birds is via radiotracking.
However, radio-tracking nonterritorial
birds would require large samples of juveniles to
be marked with radios, and these radios replaced
on the birds as necessary to maintain the batteries
as long as the individual remained in the
nonterritorial population. Placing radios on
spotted owls may alter their behavior and/or
survival (Paton et al. 1991, Foster et al. 1992),
making such an approach of questionable value.
Thus, the Team concludes that no viable method
of monitoring nonterritorial birds is available.
An alternative approach to monitoring
populations was considered, that of using demographic
study areas. We decided against using
demographic studies for three reasons.
First, demographic study areas suffer from a
deficiency that is not inherent in the quadrat
place procedure described in III.C. Demographic
study areas are chosen at the beginning
of the monitoring period and must remain in
place to provide appropriate data to meet their
objectives. Because these study areas must be
permanently delimited, management practices
on them may not reflect those occurring on
other lands. In contrast, quadrats can be randomly
replaced in the sample to ensure that
habitat changes and management practices
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Mexican Spotted Owl Recovery Plan
adequately reflect those occurring on lands
outside of the quadrats.
Second, the cost of demographic study areas
probably exceeds the cost of our proposed
quadrat monitoring approach. The cost of
conducting five demographic studies for the
California spotted owl is roughly equivalent to
the estimated cost of quadrat monitoring (J.
Verner, FS, PSW, Fresno, pers. comm). More
than five demographic study areas would be
needed for a valid population monitoring
scheme, thus putting the cost of demographic
study areas well above the costs of the proposed
quadrat sampling procedure.
Finally, the two existing demographic study
areas were not randomly selected from all possible
demographic areas (thus not providing a
defendable sample). Thus, results from the
existing demography studies apply only to the
place where these studies were done. Further,
even if a demographic study approach was used,
these existing study areas may not be included in
the random sample needed for a statisticallydefensible
monitoring scheme.
The problems outlined above with respect to
using demographic studies for monitoring do
not negate the usefulness of such studies. Demographic
studies were designed to understand
aspects of spotted owl population biology and
provide a wealth of information on populations,
habitat characteristics, and parameters of owl
fitness. They were not designed to monitor
large-scale population trends.
Monitoring Monitoring Monitoring Habitat Habitat Trends
Trends
Ganey and Dick (1995) demonstrate that
the Mexican spotted owl uses specific habitat
characteristics. These features vary geographically,
but within pine-oak and mixed-conifer
forests spotted owls use areas that contain large
trees, snags, high log volume, multistoried stand
structure, and other specific attributes. Presently,
habitat trends for the Mexican spotted owl are
unknown, and the subject of conflicting speculation
(II.D). Clearly, adequate habitat of sufficient
quality must exist into the future to ensure
population viability. Consequently, habitat
monitoring is an essential part of the recovery

process and the bird should not be delisted until
monitoring can ensure unequivocally that
sufficient habitat exists to support a viable
population of spotted owls.
Habitat monitoring should address two
aspects: persistence of forest types that owls
prefer (macrohabitat) and specific habitat attributes
within those types (microhabitat). This
roughly corresponds to the coarse and fine filters
described in II.D.
The first task, then, is to quantify large-scale
changes in macrohabitat across the range of the
bird. Given existing high fire risks and the
current state of southwestern forests, we expect
that net macrohabitat change over the next 10
years will be negative. Although some areas will
develop into habitat as the result of succession
and past management activities, the Team
assumes that (1) most acreage currently on a
trajectory to become habitat will not do so
during the life of the plan, and (2) some habitat
will be lost to fire during the next 10-15 years
(II.D). Thus, the Team anticipates a slight
decline in the total acreage of spotted owl
macrohabitat during the short term. Unfortunately,
we cannot specify a priori a threshold
level of habitat loss that the spotted owl population
can safely endure. That relationship can
only be evaluated by combining the results of
population and habitat monitoring.
The second task for habitat monitoring is to
evaluate whether or not management prescriptions
were implemented effectively, and whether
treated stands will remain or become owl habitat
in the near future. Prescriptions pertain primarily
to the use of prescribed fire and various
silvicultural tools. Monitoring to meet this
objective would entail pre-treatment sampling to
measure existing habitat attributes, and posttreatment
sampling to verify that the prescription
met the intent of the treatment. Attributes
to be sampled include both those typically
measured during stand examinations and also
additional variables not typically measured but
that are strong correlates of owl presence (e.g.,
canopy cover, log volume). The general design
for measuring owl habitat can be modified to
monitor other ecosystem attributes as well. That
is, additional variables can be measured besides
those needed for spotted owls as required for
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Mexican Spotted Owl Recovery Plan
other ecosystem management objectives. These
types of coordinated efforts will be crucial to
meeting the monitoring needs inherent to both
ecosystem and adaptive management.
Long-term Long-term Management Management Plan
Plan
As described in Part I, this Recovery Plan is
intended to guide management for Mexican
spotted owls over the next 10-15 years. If implemented
as recommended, significant research
will be conducted during this period and important
new information will become available,
specifically data on owl biology, population
structure, and effects of certain management
practices on owl habitat. Further, the guidelines
that we propose for managing restricted areas
(III.B) will provide a foundation upon which
long-term management might be based. Evaluation
of this approach and the information
provided through research and monitoring will
be integral to developing and refining a longterm
plan for managing the Mexican spotted
owl. Such a plan will be required before delisting
can be considered.
Delisting Delisting at at the the RU RU Level
Level
The Team recommends that once the population
and habitat are shown to be stable or
increasing, delisting should be considered at the
RU level. When delisting is considered, attention
must focus on the resolution of known
threats and the identification of emerging threats
that could potentially compromise population
viability. Similarly, spotted owl habitat must be
monitored in each RU to determine trends.
Monitoring will reveal habitat decline, improvement,
or relative stability. The reasoning is that if
the threats are removed or adequately regulated
and if habitat trends are stable or showing
improvement, protection under the Act will no
longer be necessary. Conversely, a habitat decline
or a lack of adequate regulatory mechanisms
(other than provided by the Act) would warrant
continued protection under the Act.
The reasoning behind monitoring population
levels within three RUs and habitat in all
RUs is as follows. A viable core population will

exist in the three RUs if the population is shown
to be stable or increasing. Therefore, if habitat
rangewide is also stable or increasing, the core
population is provided the opportunity of
expanding its area and greatly increasing the
persistence probability of the subspecies. As
discussed by Keitt et al. (1995), some key
unoccupied habitat patches are potentially
significant in the expansion of the core population.
Moderating Moderating and and Regulating Regulating Threats Threats
Threats
Threats to be moderated include those that
need site-specific treatment to alleviate them.
The primary threat throughout the forested U.S.
range of the Mexican spotted owl is the threat of
widescale, stand-replacing fire. For threats to be
considered as moderated, reasonable progress
must have been made in removing the threats
and adequate assurance, in the form of the longterm
management plan described above, must
exist that those programs will continue as necessary.
Threats to be regulated include those resulting
from agency management programs or other
anthropogenic activities that are either ongoing
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Mexican Spotted Owl Recovery Plan
or reasonably certain to occur. A partial listing of
threats besides fire include:
1. Timber or fuelwood harvest that either
directly affects habitat within a territory
or indirectly affects the owl by collateral
activity adjoining owl territories;
2. urban and rural land development;
3. livestock and wildlife grazing;
4. recreation involving both consumptive
and nonconsumptive activities.
Habitat Habitat Trends Trends Within Within Within Recovery Recovery Units
Units
For the spotted owl to be delisted within any
RU, the following conditions must be met. First,
threats to the continued loss of habitat and key
habitat components must be moderated and
regulated as detailed in the previous section.
Second, habitat trends must be monitored to
assess gross changes in habitat quantity within
each RU. Third, effects of modifying activities
within existing and potential spotted owl habitat
must be monitored to ensure that existing
habitat is maintained and potential habitat is
progressing towards becoming replacement
habitat.

The Recovery Plan recommendations are a
combination of (1) protection of both occupied
habitats and unoccupied areas approaching
characteristics of nesting habitat, and (2) implementation
of ecosystem management within
unoccupied but potential habitat. The goal is to
protect conditions and structures used by spotted
owls where they exist and to set other stands
on a trajectory to grow into replacement nest
habitat or to provide conditions for foraging and
dispersal. By necessity this Plan is a hybrid
approach because the status of the Mexican
spotted owl as a threatened species requires some
level of protection until the subspecies is
delisted. These constraints modify ways and
opportunities to manage ecosystems within
landscapes where owls occur or might occur in
the future. We are applying ecosystem management
in two slightly different ways. Within
unoccupied mixed-conifer and pine-oak forest
on

number of guiding principles. These are enumerated
below.
Assumptions
Assumptions
1. Spotted owl distribution is limited
primarily by the availability of habitat
types used for nesting and/or roosting.
2. Habitats used for nesting/roosting also
provide adequate conditions for foraging
and dispersal activities. Thus, providing
nesting/roosting habitat partially meets
other survival requirements as well. In
turn, some stand structures not used for
nesting/roosting may provide adequate
conditions for other activities such as
foraging and dispersal. These include
some stands in younger seral stages than
typical nesting/roosting habitat.
3. Nesting/roosting habitat in forest environments
is typified by certain structural
features, including large trees and late
seral characteristics, which are common
in, but not restricted to, old-growth
forests.
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Mexican Spotted Owl Recovery Plan
Figure Figure III.B.1. III.B.1. Conceptualization of the Recovery Plan and needs for delisting of the Mexican
spotted owl depicting the interdependency of population monitoring, habitat monitoring, and management
recommendations.
83
4. Forested nesting/roosting habitat is
typically found in mixed-conifer, pineoak,
and riparian forests. Other habitat
types are used primarily for foraging,
dispersal, or wintering. Thus, the distribution
of nesting/roosting habitat is
naturally discontinuous. Further, the
potential distribution of such habitat is
quite limited in some areas.
5. The presence of shade-intolerant species
in many spotted owl nest/roost stands
suggests that these areas are dynamic and
have developed over time, often from
more open stands. Disturbance events
leading to forest canopy gaps may be
important in maintaining shade-intolerant
species, particularly in mixed-conifer
stands.
6. Existing stand structures used by Mexican
spotted owls for nesting/roosting
generally have not been a target of
planned silvicultural treatments. Where
such conditions exist in managed stands,
they are more than likely an unplanned

Volume I/Part III
rather than purposeful result. The
existence of Mexican spotted owl nesting/roosting
habitat usually results from
the lack of recent alteration of forest
structures in certain landscapes.
Guiding Guiding Principles
Principles
1. Silvicultural applications must be evaluated
over time by rigorous monitoring
procedures to assess their effectiveness in
managing or creating owl habitat.
2. Obtaining large trees is a function of
both time and site productivity. Similarly,
many late seral characteristics
typical of owl habitat, such as brokentopped
trees, snags, large downed logs
and the sharing of growing space among
multiple shade-tolerant and intolerant
species, are attained primarily through
time.
3. Although this Recovery Plan represents a
short-term strategy, management actions
recommended herein will have longterm
consequences. Therefore, care
should be taken to preserve future
options while evaluating the effectiveness
of proposed treatments.
GENERAL GENERAL RECOMMENDATIONS
RECOMMENDATIONS
General management recommendations for
use throughout the range of the Mexican spotted
owl are given here. These general recommendations
apply primarily to forested areas, and
aspects of the recommendations are more applicable
to some locations than others. Because the
severity of potential threats varies among RUs,
the general guidelines should be prioritized and
applied accordingly. Specific management
priorities are emphasized in sections on individual
RUs, as warranted by the differences
among RUs.
Three levels of habitat management are
given in this Recovery Plan: protected areas,
restricted areas, and other forest and woodland
types (Figure III.B.2). Protected areas receive the
highest level of protection under this plan, other
84
Mexican Spotted Owl Recovery Plan
forest and woodland types the lowest. Guidelines
proposed in this Recovery Plan take precedence
over other agency management guidelines in
protected areas. Guidelines for restricted areas
are less specific and operate in conjunction with
ecosystem management and existing management
guidelines. We propose no owl-specific
guidelines for lands not included in protected
and restricted areas; these areas will continue to
be managed under existing guidelines, assuming
that the emphasis is towards ecosystem management.
One guideline that applies to all areas with
any potential for owl use is to inventory for
spotted owls before implementing any management
action that will alter habitat structure. If
results of past inventory efforts can demonstrate
unequivocally that no spotted owls have been
detected within a given area or habitat and that
the probability of detecting a bird there is small,
then future surveys may not be needed. Under
such circumstances, concurrence must be
granted by the Recovery Team through the
appropriate RU working team.
Protected Protected Areas Areas
Areas
Protect all Mexican spotted owl sites known
from 1989 through the life of the Recovery Plan
(Protected Activity Centers), all areas in mixedconifer
and pine-oak types (defined in II.C) with
slope >40% where timber harvest has not occurred
in the past 20 years, and all legally and
administratively reserved lands. Specific guidelines
and the rationale for these guidelines are
provided below.
Protected Protected Activity Activity Center Center (PAC)
(PAC)
Guidelines.—
Guidelines.—Eight Guidelines.— specific guidelines pertain to
the designation and implementation of PACs.
These guidelines supersede steep slope guidelines;
that is, steep slopes occurring within PACs
should be managed under PAC guidelines.
1. Establish PACs at all Mexican spotted
owl sites known from 1989 through the
life of the Recovery Plan, including new
sites located during surveys. PACs should
also be established at any historical sites
within the Colorado Plateau, Southern
Rocky Mountains - Colorado, and

Volume I/Part III
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e III.B.2. III.B.2. Generalization of protection strategies by forest/vegetation type. Proportions are not
to scale.
85

Volume I/Part III
Southern Rocky Mountains - New
Mexico RUs. Identify the activity center
within each PAC. “Activity center” is
defined as the nest site, a roost grove
commonly used during the breeding
season in absence of a verified nest site,
or the best roosting/nesting habitat if
both nesting and roosting information
are lacking. Site identification should be
based on the best judgement of a biologist
familiar with the area. Delineate an
area no less than 243 ha (600 ac) around
this activity center using boundaries of
known habitat polygons and/or topographic
boundaries, such as ridgelines, as
appropriate (Figure III.B.3). The boundary
should enclose the best possible owl
habitat, configured into as compact a
unit as possible, with the nest or activity
center located near the center. This
should include as much roost/nest
habitat as is reasonable, supplemented by
foraging habitat where appropriate. For
example, in a canyon containing mixedconifer
on north-facing slopes and
ponderosa pine on south-facing slopes, it
may be more desirable to include some
of the south-facing slopes as foraging
habitat than to attempt to include 243
ha (600 ac) of north-slope habitat. In
many canyon situations, oval PACs may
make more sense than, for example,
circular PACs; but oval PACs could still
include opposing canyon slopes as
described above. All PACs should be
retained for the life of this Recovery
Plan, even if spotted owls are not located
there in subsequent years. A potential
exception to this rule is described in #8
below. Feedback on PAC delineation
should be provided to managers through
RU working groups (see Part IV). PAC
boundaries may not overlap.
2. No harvest of trees >22.4 cm (9 in) dbh
is allowed in PACs. Harvest of any trees
is only permitted as it pertains to 5
below.
3. Fuelwood harvest within PACs should be
managed in such a way as to minimize
86
Mexican Spotted Owl Recovery Plan
effects on the owl, its prey, and their
habitats. The most effective management
to meet these objectives may be to
prohibit such harvest. However, we
recognize that it may be virtually impossible
to enforce such a prohibition and
restrict access to all PACs for fuelwood
harvest. When fuelwood harvest in PACs
is unavoidable, we advocate the use of
various forms of management that can
regulate access to PACs and to the types
of fuels harvested. Potential forms of
fuelwood management include road
closures, prohibiting harvest of important
tree species such as oaks, prohibiting
harvest of key habitat components such
as snags and large downed logs (>30 cm
[12 inch] midpoint diameter), and
encouraging the harvest of small diameter
conifers in accord with 5c below.
Prohibiting fuelwood harvest of key
habitat components such as oaks, snags,
and large logs should be applied both
inside and outside of PACs to ensure that
these special components remain on the
landscape.
4. Road or trail building in PACs should
generally be avoided but may be allowed
on a case-specific basis if pressing management
reasons can be demonstrated.
5. Implement a program consisting of
appropriate treatments to abate fire risk.
The intent of this program is to assess
the combined effects of thinning and fire
on spotted owls and their habitat. The
program should be structured as follows:
a) Select up to 10% of the PACs within
each RU that exhibit high fire risk
conditions. Nest sites must be known
within these PACs. Ideally, a paired
sample of PACs should be selected to
serve as control areas.
b) Within each selected PAC,
designate 40 ha (100 acres)
centered around the nest site.
This nest area should include
habitat that resembles the structural

Volume I/Part III
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e III.B.3. III.B.3. Examples of protected activity center (PAC) boundaries from the Lincoln National
Forest. Prepared by D. Salas and L. Cole, Lincoln NF.
87

Volume I/Part III
and floristic characteristics of the
nest site. These 40 ha (100 acres) will
be deferred from the treatments
described below.
c) Within the remaining 203 ha (500
acres), combinations of thinning
trees 30 cm [12
inches] midpoint diameter), grasses
and forbs, and shrubs. These habitat
components are strong correlates of
the presence of many key prey
species of the owl. Emphasis of the
spatial configuration of treatments
should be to mimic natural mosaic
patterns.
d) Treatments can occur only during
the nonbreeding season (1 September-28
February) to minimize any
potential deleterious effects on the
owl during the breeding season.
e) Following treatments to 10% of the
PACs, effects on the owl, prey
species, and their habitats should be
assessed. If such effects are nonnegative,
an additional sample of
PACs may be treated. If negative
effects are detected, these effects
must be carefully evaluated. If they
can be ameliorated by modifying
treatments, those modifications
should occur prior to treatment of
additional PACs. If not, no additional
treatments should be permitted.
6. Within the remaining PACs, light
burning of ground fuels may be allowed
within the 500 acres surrounding the
100-acre PAC centers (5b above), following
careful review by biologists and fuels
management specialists on a case-specific
basis. Burns should be designed and
88
Mexican Spotted Owl Recovery Plan
implemented to meet the objectives
noted in 5c above. Burns should be done
only during the nonbreeding season
(1 September-28 February).
7. Within PACS treated to reduce fire risk,
either by the use of prescribed fire alone
or in conjunction with mechanical
removal of stems and ground fuels, preand
post-treatment assessments (i.e.,
monitoring) of habitat conditions and
owl occupancy must be done. Specific
habitat characteristics that should be
monitored include fuel levels, canopy
cover, snag basal area, volume of large
logs (>30 cm [12 inch] midpoint diameter),
and live tree basal area.
8. If a stand-replacing fire occurs within a
PAC, timber salvage plans must be
evaluated on a case-specific basis. In all
cases, the PAC and a buffer extending
400 m from the PAC boundary must be
surveyed for owls following the fire. A
minimum of four visits, spaced at least
one week apart, must be conducted
before non-occupancy can be inferred. If
the PAC is still occupied by owls or if
owls are nearby (i.e., within 400 m of the
PAC boundary), then the extent and
severity of the fire should be assessed and
reconfiguration of the PAC boundaries
might be considered through section 7
consultation. If no owls are detected,
then section 7 consultation should be
used to evaluate the proposed salvage
plans. If informal consultation cannot
resolve the issue within 30 days, the
appropriate RU working team should be
brought into the negotiations.
Salvage logging within PACs should
be the exception rather than the rule.
The Recovery Team advocates the
general philosophy of Beschta et al.
(1995) for the use of salvage logging. In
particular: (1) no management activities
should be undertaken that do not
protect soil integrity; (2) actions should
not be done that impede natural recovery
of disturbed systems; and (3) salvage

Volume I/Part III
activities should maintain and enhance
native species and natural recovery
processes. Further, any salvage should
leave residual snags and logs at levels and
size distributions that emulate those
following pre-settlement, stand-replacing
fires. Scientific information applicable to
local conditions should be the basis for
determining those levels.
Rationale Rationale.—The Rationale primary objective to be
achieved by these guidelines is to protect the best
available habitat for the Mexican spotted owl,
while maintaining sufficient flexibility for land
managers to abate high fire risks and to improve
habitat conditions for the owl and its prey. We
assume that the best available owl habitat is that
which is currently occupied by owls, or that
occupied by owls in the recent past (since 1989).
The median size of the adaptive kernel contour
enclosing 75% of the foraging locations for 14
pairs of radio-marked owls was 241 ha (595 ac).
Therefore, a 243 ha (600 ac) PAC should
provide a reasonable amount of protected
habitat and should provide for the nest site,
several roost sites, and the most proximal and
highly used foraging areas. We assume that
existing management guidelines and those
discussed below for areas outside of PACs will
ensure the existence of additional habitat appropriate
for foraging.
The intent of these guidelines is not to
preserve these PACs forever, but rather to
protect them until it can be demonstrated that
we can create replacement habitat through active
management. We describe below in the section
covering restricted areas the approach for managing
to create replacement habitat. Once land
managers demonstrate that they can create
replacement habitat, and when monitoring
indicates that populations and habitats are stable
or increasing, PACs could be abolished in
conjunction with delisting the owl.
The Team recognizes that protection status
carries some risk with respect to probabilities of
catastrophic fire. The reason for the proposed
management within PACs is to encourage a
proactive approach to reduce fuel risks and
simultaneously enhance prey habitat. If these
objectives are achieved, existing owl habitat will
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Mexican Spotted Owl Recovery Plan
be maintained and in some cases enhanced,
while identified risks of catastrophic fire will be
lessened.
Salvage logging in PACs should be allowed
only if sound ecological justification is provided
and if the proposed actions meet the intent of
this Recovery Plan, specifically to protect existing
habitat and accelerate the development of
replacement habitat. Fires within PACs are not
necessarily bad. In many cases, patchy fires will
result in habitat heterogeneity and may benefit
the owl and its prey. In such cases, adjustments
to PAC boundaries are probably unnecessary and
salvage should not be done. Salvage should be
considered in PACs only when the fire is extensive
in size and results in the mortality of a
substantial proportion of trees.
Steep Steep Slopes Slopes Slopes (outside (outside of of PACs) PACs)
PACs)
Guidelines Guidelines.—Within Guidelines mixed-conifer and pineoak
types, allow no harvest of trees >22.4 cm (9
inches) on any slopes >40% where timber
harvest has not occurred in the past 20 years.
(Mixed-conifer and pine-oak types found on
steep slopes that have been treated within the
past 20 years are managed under restricted area
guidelines below). These guidelines also apply to
the bottoms of steep canyons. Thinning of trees
30 cm midpoint diameter), and live tree basal
area.
Rationale ationale ationale.—The ationale objective of prohibiting timber
harvest but allowing treatment of fuels and
burning is to retain additional habitat with
existing conditions similar to owl nesting/
roosting habitat while reducing fire risks. These

conditions appear to be found commonly in
mature/old-growth stands, and such stands are
now found most commonly on steep slopes
because past management practices have largely
occurred on slopes

succession. The landscape mosaic resulting from
such an allocation should ensure adequate
nesting, roosting, and foraging habitat for the
owl, and habitats for its variety of prey.
Existing Existing Conditions
Conditions
Ideally, assessments of existing conditions
should follow the spatial hierarchy presented by
Kaufmann et al. (1994:6). At the very least,
existing distributions of seral stages should be
assessed at the planning level, landscape, subregional,
and regional scales (sensu Kaufmann et al.
1994). We recognize that information may be
inadequate to conduct assessments at larger
spatial scales, but this constraint should be
ameliorated as resource agencies continue to
acquire appropriate data. Existing vegetative
conditions within mature-old stands must also
be assessed to determine the treatment potentials
within those stands. However, given the high
frequency of recent stand-altering disturbances,
many areas are likely deficient in mature to oldgrowth
forests. Thus, any treatments to these
stands should be applied judiciously, if at all.
Reference Reference Conditions
Conditions
Nesting Nesting and and roosting roosting target/threshold
target/threshold
conditions conditions.—Forested conditions stands used by spotted
owls have certain structural features in common.
These conditions do not, nor can they, occur
everywhere. For example, many south-facing
slopes may never attain this type of forest structure.
It is impossible for us to imagine every
possible management scenario, and this limits
our ability to formulate specific guidelines that
would be appropriate to all situations. Our
intent here is to protect appropriate nesting
habitat structure where it exists and manage
other stands to develop the needed structure.
Although our knowledge of spotted owl
habitat is incomplete, nesting/roosting stands
exhibit certain identifiable features, including
high tree basal area, large trees, multi-storied
canopy, high canopy cover, and decadence in the
form of downed logs and snags (Ganey and Dick
1995). Further, these stands often contain a
considerable hardwood component generally
provided by Gambel oak in ponderosa pine-
Gambel oak forests and by various species (e.g.,
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Mexican Spotted Owl Recovery Plan
oaks, maples, box elder, aspen) in mixed-conifer
forests.
We used tree basal area, large tree (>45.7 cm
[18 in] dbh) density, and tree size-class distribution
as the variables to define target/threshold
conditions (Table III.B.1). Other variables such
as snags and downed logs are important as well.
We assume that if the basal area and tree density
levels given in Table III.B.1 exist, adequate
amounts of snags and downed logs (and other
habitat elements) should be present.
The values provided in Table III.B.1 represent
targets in that they define the desired
conditions to be achieved with time and management.
They also represent threshold conditions
in that they define minimal levels that
must be maintained. That is, activities can occur
within stands that exceed these conditions, but
the outcome of such activities cannot lower the
stands below the threshold levels unless largescale
ecosystem assessments demonstrate that
such conditions occur in a surplus across the
landscape (see below). Note that all values must
be met simultaneously for a stand to meet target/
threshold conditions.
We used two primary types of information
to define target/threshold conditions. First, we
used quantitative descriptions of site- and standlevel
habitat conditions. Second, we estimated
the proportion of the landscape that could
sustain those conditions through time. A similar
approach was provided for managing northern
goshawk habitat in the southwest (Reynolds et
al. 1992). Thus, our approach is not without
precedence.
Despite repeated attempts by the Recovery
Team to obtain data from land-management
agencies and researchers, only limited data were
available for our analyses. We used nest-site data
collected by SWCA (1992) which included plot
measurements centered (1) at each nest location,
(2) a random location within each nest stand,
and (3) a random location within a stand adjacent
to the nest stand (see Ganey and Dick
[1995] for more detailed information). We also
used FS stand inventory data provided by the
Coconino, Apache-Sitgreaves, and Lincoln
National Forests. These data consisted of standlevel
data stratified by nest, core, and territory
stands. Core and territory delineations were

92
Table Table III.B.1. III.B.1. Target/threshold conditions for mixed-conifer and pine-oak forests within restricted areas. Forest types are defined in II.C.

ased on FS management guidelines for the
Mexican spotted owl provided by ID No. 2 (see
Part I). We had no way to assess the accuracy of
the data. Different methods were used to collect
the SWCA data from those used to collect the
FS data, thus direct comparisons are tenuous.
Neither data set was collected specifically to
address our objectives; thus, the data were less
than optimal for our purposes. Further, numerous
people collected data and we cannot assess
inter-observer variation (Block et al. 1987). As
obvious as these points may be, they greatly
limited the inferences that we could make based
on our analyses. Thus, we relied on our best
professional judgement to evaluate the analyses
and formulate our recommendations.
We explored several analyses to derive target/
threshold conditions including empirical
univariate and multivariate analyses, and modeling.
Most analyses converged on a set a values
that were validated by existing data on spotted
owl nesting habitat.
We used the following approach. First, we
used the SWCA (1992) data to characterize nest
stands on the basis of tree basal area, density of
large trees, and the distribution of stand density
by size classes. Next, we used the available FS
stand data to identify the percentage of the
contemporary landscape that simultaneously
meets these values. Third, we modeled forest
stands under various post-disturbance/stand
initiation conditions using the Forest Vegetation
Simulator (Wykoff et al. 1982, Dixon 1991,
Edminster et al. 1991). This model allowed us to
predict the amount of time that a stand would
be in each successional stage, including the
amount of time the stand would retain or exceed
the characteristics required for nesting and
roosting. Knowledge of how long a stand meets
or exceeds target conditions was used to estimate
the proportion of the landscape that should meet
or exceed these stand conditions at a given time.
Analyses were conducted separately for
mixed-conifer and pine-oak forests. We also
provide two sets of values for mixed-conifer
forest that reflect different target/threshold
values which are applied to different proportions
of the landscape (Table III.B.1). We reiterate
that all target/threshold values must be met
simultaneously. For example, within mixed-
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Mexican Spotted Owl Recovery Plan
conifer forests in all RUs except Basin and Range
- East, 25% of the landscape should consist of
stands that have >32 m 2 /ha (150 ft 2 /acre) of tree
basal area, and include >49 trees/ha (20 trees/
acre) that are >45.7 cm (18 inches) dbh. Management
should strive for an even distribution of
stand density across all sizes classes with no less
than 10% of the distribution of stand density in
each of the upper three size classes: 30.5-45.7 cm
(12-18 inches), 45.7-61.0 cm (18-24 inches),
and >61.0 cm (24 inches). Also, 10% of the total
landscape (a subset contained within the 25%
discussed above), should have >39 m 2 /ha (170
ft 2 /acre) of basal area in addition to the large
trees and distribution of trees by size class.
Target/threshold conditions for mixed-conifer
forests in the Basin and Range - East RU differ
slightly in that landscape percentages are 20%
and 10%. The areal percentage for Basin and
Range - East RU is lower (20% compared to
25%) because of the high density of owls in the
Sacramento Mountains which effectively places a
large proportion of the landscape in protected
status. Target/threshold conditions apply to only
10% of the pine-oak forest (Table III.B.1).
Target/threshold conditions for pine-oak forests
also require that >4.6 m 2 /ha (20 ft 2 /acre) of oak
basal area be present, and that all oaks >13 cm [5
inches] dbh be retained (Table III.B.1).
Coarse Coarse Filter
Filter
We recognize that most project planning
occurs at limited spatial scales such as 4,050 ha
(10,000 acre) blocks. This limited spatial scale
precludes ecological assessments at larger scales.
Because of this limitation, the areal percentages
provided in Table III.B.1 should be regarded as
minimum levels for a given planning area. If a
deficit occurs within the planning area, additional
stands should be identified that (1) have
the site potential to reach target conditions and
(2) whose current conditions most closely
approach those conditions. Those stands should
then be managed to achieve target conditions as
rapidly as possible. However, if the proportion of
the planning area that meets target conditions is
greater than the percentages in Table III.B.1,
none of those stands can be lowered below
threshold conditions until ecosystem assessments
at larger spatial scales (landscape, subregion,

egion) demonstrate that target conditions
exceed the required areal percentages (Table
III.B.1) at these larger scales. This does not
preclude use of treatments to reduce fire risks or
lessen insect or disease problems nor does it
preclude management to meet other ecosystem
objectives as long as stand-level conditions
remain at or above the threshold values given in
Table III.B.1.
Fine Fine Filter Filter
Filter
Overriding Overriding Guidelines Guidelines.—Management Guidelines
activities
that influence the owl and its habitat should be
conducted according to the following overriding
guidelines:
1. Manage mixed-conifer and pine-oak
forest types to provide continuous
replacement nest habitat over space
and time. Treatment of a particular
stand depends on its capability to attain
the desired stand conditions. Target
stand structure would be the described
conditions for nesting and roosting
habitat (Table III.B.1) but only the
portion of the landscape that can be
sustained through time should be in
that condition.
2. Incorporate natural variation, such as
irregular tree spacing and various stand/
patch sizes, into management prescriptions
and attempt to mimic natural
disturbance patterns.
3. Maintain all species of native vegetation
in the landscape, including early seral
species. To allow for variation in existing
stand structures and provide species
diversity, both uneven-aged and evenaged
systems may be used as appropriate.
4. Allow natural canopy gap processes to
occur, thus producing horizontal variation
in stand structure.
Specific Specific Guidelines Guidelines—The Guidelines following guidelines
are intended to minimize threats to the Mexican
spotted owl, retain and enhance important but
difficult-to-replace habitat elements, and provide
management flexibility.
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Mexican Spotted Owl Recovery Plan
1. Emphasis should be placed on unevenaged
management systems. Existing
stand conditions will determine which
silvicultural system is appropriate.
2. Extend rotation ages for even-aged
stands to >200 years. Silvicultural prescriptions
should explicitly state when
vegetative manipulation will cease until
rotation age is reached. This age may
depend on site quality, but ceasing
activity at 140 years and allowing 60
years for unaltered stand maturation and
senescence seems reasonable.
3. Within pine-oak types, emphasis should
be placed on management that retains
existing large oaks and promotes the
growth of additional large oaks.
4. Retain all trees >61 cm [24 in] dbh.
5. Retain hardwoods, large down logs, large
trees, and snags.
6. Management priority should be placed
on reducing identified risks to spotted
owl habitat. The primary existing threat
is catastrophic wildfire. Thus, we
strongly encourage the use of prescribed
and prescribed natural fire to reduce
hazardous fuel accumulations. Thinning
from below may be desirable or necessary
before burning to reduce ladder fuels and
the risk of crown fire. Such thinning
must emphasize irregular tree spacing.
7. No stand that meets threshold conditions
can be treated in such a way as to
lower that stand below those conditions
until ecosystem assessments can document
that a surplus of these stands exist
at larger landscape levels (e.g., no less
than the size of a FS District). This does
not preclude use of treatments to reduce
fire risks or lessen insect or disease
problems, nor does it preclude management
to meet other ecosystem objectives
as long as stand-level conditions remain
at or above the threshold values given in
Table III.B.1.

Rationale Rationale Rationale.— Rationale Rationale .— .—The .— collective goal of these general
and specific guidelines is to provide spotted owl
habitat that is well distributed over space and
time. To accomplish this goal requires maintaining
or creating stand structures typical of nesting
and roosting habitats and sustaining them in
sufficient amounts and distribution to support a
healthy population of Mexican spotted owls. A
few guidelines merit further comment.
Retaining large trees is desirable because they
are impossible to replace quickly and because
they are common features of nesting and roosting
habitats for the owl. Fire, viewed as a natural
formative process rather than as a destructive
anthropogenic process, can be used advantageously
to maintain or improve spotted owl
habitat.
The guidelines presented above should not
be misconstrued as onetime management events.
For example, large trees and snags are required
by the spotted owl and will continue to be
needed by the owl in the future. Further, the
approach outlined above provides a foundation
for the development of a long-term management
strategy. Once the owl is delisted, we expect that
this general template can be evaluated, finetuned,
and possibly applied to PACs and steep
slopes.
Riparian Riparian Communities
Communities
Guidelines Guidelines.—
Guidelines .— .—The .— goals of these guidelines are
to maintain healthy riparian ecosystems where
they exist and initiate restoration measures to
return degraded areas to healthy conditions.
1. Maintain riparian broad-leaved forests in
a healthy condition where they occur,
especially in canyon-bottom situations.
Where such forests are not regenerating
adequately, active management may be
necessary. Possible actions to restore
these forests may include reducing
grazing pressure, establishing riparian
exclosures to manage forage use better,
and shifting to winter grazing seasons.
2. Restore lowland riparian areas. Spotted
owls once nested in riparian gallery
forests. Conceivably, restored riparian
forests could contribute additional
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Mexican Spotted Owl Recovery Plan
nesting habitat in the future and could
also create a landscape that is more
effectively connected for dispersing owls.
3. Emphasize a mix of size and age classes
of trees. The mix should include large
mature trees, vertical diversity, and other
structural and floristic characteristics that
typify natural riparian conditions.
Rationale Rationale.— Rationale .— .—We .— assume that riparian forests
provide important habitat for spotted owls.
Many riparian systems within the range of the
Mexican spotted owl are extremely degraded as
the result of past management practices. Because
many of these systems are degraded and little
documentation of recent owl use exists, we have
little empirical information upon which to
provide specific guidelines. Thus, our underlying
premise is that if riparian systems are restored to
more natural conditions, the needs of the owl
(and numerous other species) will be satisfied.
This is particularly true in canyon-bottom
situations at middle and lower elevations where
little other typical nesting or roosting habitat
may be available. We know that canyon bottoms
are used extensively by the owl, thus it is important
to preserve and increase the quality of such
habitat. We anticipate that PACs will include
some of the best of this type of habitat that still
exists, but increasing the quantity and distribution
of healthy riparian habitats provides the
potential for increasing spotted owl habitat.
Furthermore, maintenance of existing healthy
riparian systems and restoration of those that are
degraded will benefit numerous riparian-dependent
flora and fauna, and ecosystem health
across the landscape.
Other Other Forest Forest and and Woodland Woodland Types
Types
We propose no specific guidelines for several
forest and woodland community types where
they occur outside PACs. These include ponderosa
pine, spruce-fir, pinyon-juniper, and aspen
as defined in II.C. We emphasize, however, that
the lack of specific management guidelines
within this plan does not imply that we regard
these types as unimportant to the Mexican
spotted owl.

The Team’s rationale for these recommendations
is based on extant information on the
natural history of the Mexican spotted owl as
summarized in Part II.A and detailed in Volume
II. These forests and woodlands are not typically
used for nesting and roosting. However, they
may provide habitat for foraging and possibly for
both dispersing and wintering spotted owls. Our
grasp of the owl’s natural history regarding these
behaviors is incomplete, so we do not fully
understand the structural features the owl
requires for pursuing these activities in these
forest and woodland types. Furthermore, some
of the best foraging habitat should be protected
in PACs. All of these circumstances allow us to
be less restrictive in these community types
without harming the owl or compromising its
primary habitat.
With the exception of the acreage of these
types contained within PACs, we assume that
the remaining lands are used primarily for
foraging, wintering, migration, and dispersal.
Thus, we contend that existing and planned
management for these types will maintain or
improve habitat for these needs of the owl. This
contention is based largely on the assumption
that existing old-growth areas will be maintained
across the landscape, silvicultural practices will
favor selection over regeneration cuts, and
management will be guided by ecosystem
approaches that strive to provide sustainable
conditions across the landscape that fall within
the natural range of variation.
Guidelines developed for protected and
restricted areas may have useful applications
when judiciously administered in these other
forest and woodland types. Such guidelines
include managing for landscape diversity, mimicking
natural disturbance patterns, incorporating
natural variation in stand conditions, retaining
special features such as snags and large trees,
and utilizing fires as appropriate. We also emphasize
the need for proactive fuels management
where appropriate. Decreasing fire risks within
these types, particularly ponderosa pine forests,
will also decrease fire risks to adjoining protected
and restricted areas by minimizing the probability
of large landscape-level crown fires that could
impinge upon occupied or potential nesting
habitat.
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GRAZING GRAZING RECOMMENDATIONS
RECOMMENDATIONS
The explicit goals of managing grazing in
spotted owl habitat reflect the four manifested
influences of grazing discussed in II.D. Those
influences were (1) altered prey availability, (2)
altered susceptibility to fire, (3) degeneration of
riparian plant communities, and (4) impaired
ability of plant communities to develop into
spotted owl habitat. The goals then become (1)
to maintain or enhance prey availability, (2) to
maintain potential for beneficial ground fires
while inhibiting potential for destructive standreplacing
fire, (3) to promote natural and
healthy riparian plant communities, and (4) to
preserve the processes that ultimately develop
spotted owl habitat.
The Team strongly advocates field monitoring
and experimental research related to the
impacts of grazing on the Mexican spotted owl.
Only through monitoring and research can we
(1) develop a comprehensive understanding of
how grazing affects the habitat of the owl and its
prey; (2) determine the effectiveness of current
grazing standards and guidelines as they relate to
the owl’s needs; and (3) devise grazing strategies
that can benefit the owl and its prey.
Grazing Grazing Guidelines Guidelines
Guidelines
The following guidelines should be applied
to all protected and restricted areas:
1. Monitor grazing use by livestock and
wildlife in “key grazing areas.” Key
grazing areas are primarily riparian areas,
meadows, and oak types. Monitoring
should begin by determining current
levels of use plus current composition,
density, and vigor of the plants. Ultimately,
monitoring should detect any
change in the relative composition of
herbaceous and woody plants. The intent
is to maintain good to excellent range
conditions in key areas while accommodating
the needs of the owl and its prey.

2. Implement and enforce grazing utilization
standards that would attain good to
excellent range conditions within the key
grazing areas. Use standards (e.g., FS
Region 3, Range Analysis Handbook)
that have been developed for local
geographic areas and habitat types-particularly
in key habitats such as
riparian areas, meadows, and oak types-that
incorporate allowable use levels
based on current range condition, key
species, and the type of grazing system.
Establish maximum allowable use levels
that are conservative and that will
expedite attaining and maintaining good
to excellent range conditions. The
purpose of establishing these use levels is
to ensure allowable use of plant species
to maintain plant diversity, density,
vigor, and regeneration over time.
Additionally, a primary purpose is to
maintain or restore adequate levels of
residual plant cover, fruits, seeds, and
regeneration to provide for the needs of
prey species and development of future
owl foraging and dispersal habitat.
3. Implement management strategies that
will restore good conditions to degraded
riparian communities as soon as possible.
Strategies may include reductions in
grazing levels and increased numbers of
exclosures (i.e., fencing) to protect
riparian plant cover and regeneration,
and to prevent damage to stream banks
and channels (Clary and Webster 1989,
Platts 1990). In many cases, degraded
riparian areas may require complete rest
for periods from a few years to 15 years
for the area to recover (Kennedy 1977,
Rickard and Cushing 1982, Clary and
Webster 1989). Additional strategies may
include the use of riparian pastures,
limited winter use, double rest-rotation,
and other methods that emphasize
riparian vegetation and stream bank/
channel recovery (Platts 1990). Riparian
restoration projects that include the use
of exclosures need not require exclosures
along the entire drainage course at one
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time. Rather, systematic use of exclosures
that protect the most sensitive portions
of riparian habitats is encouraged.
Riparian areas can also benefit from
protection of adjacent upland areas
(Bryant 1982). Placement of exclosures
(controls) and areas open to grazing
(treatments) should be designed to
permit determination of effects on
several ecological responses (e.g., vegetation,
erosion, water quality, prey availability).
Rationale Rationale for for for Grazing Grazing Guidelines
Guidelines
Some effects of excessive grazing on vegetation
and habitat features are predictably negative,
particularly in riparian communities.
However, the collective effects of grazing are
neither always predictable nor always negative.
Effects depend on site-specific factors such as the
grazing system, condition of the plant community
prior to livestock grazing, soil types, climate,
community composition of plant species, and
the presence or absence of aggressive exotic plant
species. Succinctly, predictability is inexact; and
without predictability the Team cannot give
detailed and specific recommendations.
We suggest that, when implemented and
enforced, general guidelines and the standards
they prescribe will promote and maintain good
to excellent range conditions over time and
across communities used by the owl. Despite our
imprecise knowledge of how grazing affects
spotted owl habitat, the collective body of
general knowledge regarding the impacts of
grazing on wildlife mandates prudence. The
Team believes that understanding how grazing
affects the owl is paramount, and we strongly
urge that specific grazing practices and levels of
grazing use be carefully evaluated through an
experimental approach (Bock et al. 1993).
Habitats in protected and restricted areas
should receive high-priority management attention
relative to grazing. Any riparian communities
of potential importance for spotted owl
dispersal and wintering habitat should also
receive high-priority attention. Such attention
will not only benefit spotted owls but many
other species in the Southwest as well (Hubbard

1977). Fundamental to the guidelines for
grazing is the assumption that individual actions
have collective effects. For example, the shortterm
goal of exclusion by fencing is to protect
riparian plants and to prevent physical damage
to stream banks and channels (Clary and
Webster 1989, Platts 1990). The long-term goal
is that such short-term protection ultimately
allows spotted owl habitat to develop. Implicit in
this rationale is that excessive grazing sustained
for long periods not only deteriorates potential
or actual spotted owl habitat but it also inevitably
leads to a deterioration of the very qualities
that make an area attractive for grazing in the
first place.
We also assert that attainment and maintenance
of good to excellent conditions in key
grazing areas will translate to better conditions in
the uplands. Most native and exotic ungulates
preferentially graze within key areas such as
meadows and riparian areas. We assume that if
these key areas exhibit ecologically good conditions,
upland forests and woodlands should also
be in good condition. Thus, negative effects of
grazing that lead to the establishment of ladder
fuels and “dog-hair” thickets may be ameliorated.
RECREATION
RECREATION
RECOMMENDATIONS
RECOMMENDATIONS
Guidelines
Guidelines
The following guidelines should be applied
to all protected and restricted areas:
1. No construction, either of new facilities
or for expanding existing facilities,
should take place within PACs during
the breeding season, 1 March through
31 August. Any construction within
PACs during the nonbreeding season
should be considered on a case-specific
basis. Modifications to existing facilities
pertaining to public safety and routine
maintenance are excepted.
2. Managers should, on a case-specific basis,
assess the presence and intensity of
allowable recreational activities within
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PACs. Spatial and temporal restrictions
should be considered for new activities.
3. Seasonal closures of specifically designated
recreational activities should be
considered where appropriate.
RECOVERY RECOVERY UNIT
UNIT
CONSIDERATIONS
CONSIDERATIONS
We review below primary threats within each
recovery unit. Some threats are ubiquitous across
the range of the spotted owl, whereas others are
limited to one or few RUs. To place these threats
in perspective, we review below relevant information
from Part II.B for each RU. Management
priorities within each RU should focus on
the threats identified below.
One management consideration that applies
to all RUs is the potential for migration and
dispersal of spotted owls within and among RUs.
Admittedly, we know very little of the prevalence
of such movements, nor do we know much of
the habitats used. We suspect, however, that
movements of birds may be important to gene
flow and the maintenance of a metapopulation
structure (Keitt et al. 1995). Thus, efforts should
be made to preserve options by maintaining and
enhancing potential avenues for migration and
dispersal. This could be particularly important in
specific canyons, riparian areas, and mountain
ranges that might provide links within, between,
and among RUs.
Colorado Colorado Colorado Plateau Plateau
Plateau
The Colorado Plateau is the largest of all
U.S. RUs. It encompasses the southern half of
Utah, much of northern Arizona, most of
northwestern New Mexico, and a small portion
of southwestern Colorado. In the northwestern
portion of this RU, owls have been located in
steep-walled canyons with apparent concentrations
in the areas of Zion N.P., Capitol Reef
N.P., western Abajo Mountains, and
Canyonlands N.P. Historical records are available
from forested habitats on the Kaibab Plateau of
northern Arizona. In the southeastern portion of
this RU, owls occur in both steep-sloped, mixedconifer
forested canyons and steep-walled

canyons on the Navajo Indian Reservation;
known concentrations occur in the Black Mesa
area and the Chuska Mountains. Owls have also
been located in mixed-conifer habitats in the
Zuni Mountains and on Mount Taylor (Figure
II.B.3).
Owl distribution in this RU appears to be
highly fragmented. This distributional pattern
may be natural or the result of inadequate survey
effort in some parts of the RU. Extensive surveys
have, however, been completed in the southern
Utah portion of this RU. Here, breeding owls
have been found only in canyons where they
nest and roost in caves and on ledges. In southern
Utah, no breeding owls have been located in
hundreds of thousands of hectares surveyed in
mixed-conifer or other forest types in areas with
less than 40% slope. Therefore, we recommend
that surveys in southern Utah emphasize steep
slopes and rocky canyons.
Potential Potential Threats
Threats
Levels of recreational activity are high and
increasing in some areas of this RU, such as
southern Utah. Some activities may potentially
lead to habitat alteration or direct disturbance of
owls. Furthermore, owls in southern Utah nest
and roost in canyons, and the physical structure
of canyons tend to magnify disturbances and
limit escape/avoidance routes for owls. Potential
threats listed in order of severity for the northwestern
portion of this RU include recreation,
overgrazing, and road development within
canyons, and catastrophic fire and timber harvest
within upland forests potentially used for foraging,
dispersal, and wintering. For the southeastern
portion, threats include timber harvest,
overgrazing, catastrophic fire, oil, gas, and
mining development, and recreation (Utah
Mexican Spotted Owl Technical Team 1994).
Southern Southern Rocky Rocky Mountains Mountains - - Colorado
Colorado
Lying completely within the State of Colorado,
the Southern Rocky Mountains - Colorado
represents the northeastern extreme of the
Mexican spotted owl’s range. Few owls have been
detected in this portion of its range, and its
natural history in Colorado is poorly understood.
However, the condition of a species being
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scarce at the periphery of its range is not unusual.
Nesting and roosting habitat may be
primary concerns, but wintering habitat may be
an important factor in this RU. Although very
little is known about wintering habitat, some
data suggest that birds may winter at lower
elevations that include a wider range of conditions
than found in breeding habitats.
Potential Potential Threats
Threats
In order of severity, potential threats for the
Southern Rocky Mountains - Colorado RU are
catastrophic fire, recreation, urbanization, timber
harvest, and road construction. Less severe
threats include land exchange, oil and gas
leasing, mineral development, and grazing.
Singly, these factors may have low impact, but
high synergistic consequences. For example,
much of the urban development in Southern
Rocky Mountains - Colorado currently occurs at
elevations lower than those occupied by breeding
owls; but development increases recreational
access to public lands. Road construction or
expansion causes initial disturbance, recreation
facilities extend the disturbance, and the
improved access increases the contact between
people and spotted owls. The initial activity
may directly affect wintering habitat. The
development threat is considered to be of low
to moderate severity and is highest along the
Front Range.
Southern Southern Rocky Rocky Mountains Mountains -
-
New New Mexico
Mexico
Ranking as the smallest U.S. RU, the Southern
Rocky Mountains - New Mexico supports
one of the smallest known populations of
Mexican spotted owls as well. Existing data are
too incomplete to cite even a crude estimate of
the RU’s spotted owl population or its density.
The inability to provide crude population
estimates may be partially related to the inadequacy
of existing survey protocols. Owl survey
crews, following the FS Region 3 survey protocol,
have speculated that spotted owls in the area
may not respond to calling surveys as predictably
as they do in other RUs. They base this opinion
on the lack of response to nighttime calling in
areas where owls or young have been observed

during subsequent daytime visits. Given that
surveys are an important step in designating
PACs and the types of management permissible,
it is critical that surveys have a high probability
of detecting owls. Further, an ineffective, or
partially effective, survey protocol leaves the FS
and other agencies ill-equipped to manage
potential threats to the Mexican spotted owl in
the RU.
Recent survey efforts on the Santa Fe National
Forest suggest that some areas formerly
occupied by owls appear vacant now despite the
fact that the habitat has not been altered appreciably
(T. Johnson, Las Alamos, NM, pers.
comm.). This perceived, but unconfirmed,
population decline indicates the importance of
protecting unoccupied habitat.
Potential Potential Threats
Threats
The most serious threat to spotted owls in
Southern Rocky Mountains - New Mexico RU is
wildfire and, in localized areas, timber harvest.
Fire may not be as serious in canyon systems as it
is in other areas because the open structure of
steep-slope woodlands associated with canyons
are not conducive to conflagration. However,
dense mixed-conifer and ponderosa pine forests
outside of canyons may present the greatest fire
hazards. Although these areas may not contain
owls, fires initiated in these forests may continue
into the forested canyon habitats. Personnel at
Santa Fe National Forest have instituted an
aggressive prescribed fire program in the Jemez
Mountains as a way to reduce the risk of extensive
fire. Though useful, prescribed fire should
be used conservatively in spotted owl habitat.
Timber harvest levels appear greatest on the
Carson National Forest where few spotted owls
have been confirmed. Timber harvest levels on
Santa Fe National Forest have been reduced in
areas where spotted owls are known to occur.
Isolation of spotted owl pairs and small populations
distributed over large areas of fragmented
landscape prompt concern because if they are
lost, the species disappears from entire landscapes
it once inhabited. Since the spotted owl
was listed, planned timber sales have mostly
avoided the owl’s habitat. However, in the
Vallecitos Federal Sustained Yield Unit in Carson
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National Forest, sales are still being planned in
potential spotted owl habitat despite unconfirmed
sightings of spotted owls in 1993.
Lesser threats to the spotted owl include
human activities that produce extremely localized
effects, but that may ultimately prove to
have a large collective impact. Among them are
unregulated fuelwood harvesting, grazing (particularly
in riparian areas), and recreation developments
at ski areas. All of these activities have
the potential to degrade spotted owl habitat
including habitat for the owl’s prey.
Upper Upper Gila Gila Mountains
Mountains
The Upper Gila Mountains RU contains the
largest known number of Mexican spotted owls
with approximately 55% of known spotted owl
territories (Ward et al. 1995). The owl also
appears to be more continuously distributed
across this RU than any other (II.B). The apparent
gap in owl distribution in the center of
Figure II.B.6 reflects incomplete information
from Tribal lands rather than an actual discontinuity
within the owl’s range.
Potential Potential Threats
Threats
Spotted owls throughout the RU are found
primarily in mixed-conifer and pine-oak forests
(Ganey and Dick 1995), often in conjunction
with canyon terrain. The primary threats to
spotted owls and their habitat are timber harvest
and catastrophic fire, not necessarily in that
order. Both threats could destroy forest habitat
with the structural features used by spotted owls,
and both could operate over large spatial scales.
Other threats within this RU include indiscriminate
fuelwood cutting and overgrazing by
both wildlife and livestock. These threats are not
as widespread or severe as the threats discussed
above, but they can be significant in some areas.
Fuelwood cutting is a problem in some areas
primarily because people remove (usually illegally)
large oaks. These trees appear to be critical
to owls in some areas or habitats, particularly the
pine-oak type (Ganey et al. 1992). Fuelwood
harvest can also result in loss of large snags and
down logs. Both of these habitat components are
also apparently important to the owl, either
directly or indirectly through effects on the prey

ase (Ganey and Dick 1995, Ward and Block
1995).
Overgrazing is suspected to be detrimental in
some areas and can affect both habitat structure
and the prey base. Effects on the prey base are
difficult to quantify, but removal of herbaceous
vegetation can reduce both food and cover
available to small mammals (Ward and Block
1995). This may be especially true with respect
to voles, which are often associated with dense
grass cover. Direct effects on habitat are obvious
in some places, particularly with respect to
browsing on young Gambel oak. In some areas,
oak is regenerating well but unable to grow
beyond the sapling stage because of this browsing.
Coupled with loss of large oaks to fuelwood
harvest, maintenance of most oak stems in a
sapling stage suggests a very real possibility that
large oak trees will not be replaced over large
areas, resulting in the loss of an important
habitat component. Grazing effects on habitat
are also potentially significant in canyon-bottom
riparian areas. We do not attribute these effects
solely to livestock. Forage resources are shared by
livestock and wild ungulates, and reducing
numbers of both will likely be necessary to bring
forage use to reasonable levels.
Basin Basin Basin and and Range Range - - West
West
Sprawling across southern Arizona and
extreme southwestern New Mexico, the Basin
and Range - West RU ranks as the second largest
RU in the United States. Though it probably
does not support as large a spotted owl population
as the Upper Gila Mountains RU, the
known population ranks third highest in the
United States despite limited survey efforts in
many areas. Therefore, the Team regards the
Basin and Range - West RU as an important unit
for the recovery effort.
Potential Potential Threats
Threats
The Team perceives limited threats overall to
spotted owls in the Basin and Range - West RU
as the result of human activities. Very little
timber harvest occurs in this RU, though some
timber is cut in the Bradshaw Mountains of the
Prescott National Forest and on the San Carlos
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Apache Reservation. The primary threats to
spotted owls within this RU are catastrophic
wildfire, recreation, and grazing. We detail below
the nature and extent of these and other potential
threats.
Historical efforts to suppress fire have
allowed fuel loads to accumulate to dangerous
levels within most of the wooded and forested
vegetation types in this RU. For example, the
1983 fire in the Animas Mountains removed the
coniferous forest from the higher elevations.
Recent wildfires in the Pinaleno, Rincon,
Chiricahua, and Huachuca Mountains also attest
to the volatile situation in this region. We view
the potential for catastrophic wildfire as the
primary threat to spotted owls in the Basin and
Range - West RU.
Many mountain ranges in the Coronado,
Prescott, and Tonto National Forests are used
heavily for recreation. This is partly because of
their proximity to large urban areas (Tucson and
Phoenix) and partly because of their international
reputation for exceptional birding. Effects
of recreation include development of roads,
campgrounds, and trails, and also extraordinary
use of those facilities. For example, a number of
areas within the Coronado National Forest (e.g.,
Madera Canyon in the Santa Ritas, Garden and
Ramsey Canyons in the Huachucas, and the
South Fork of Cave Creek in the Chiricahuas)
are world renowned for birding and receive
thousands of visitors per year. Scheelite Canyon
on the Fort Huachuca Army Base is visited often
by birders specifically to view the pair of spotted
owls that occur there. The Mexican spotted owl,
in fact, is one of the more popular species sought
by birders in this region.
Cattle grazing occurs throughout the RU.
Impacts are greatest in the high desert grasslands,
desert scrub, and riparian habitats found between
mountain ranges. Moderate grazing
pressures occur within mid-elevational encinal
and pinyon-juniper woodlands; and grazing
pressures are evident within higher elevational
canyon stringers of pine-oak, mixed-conifer, and
riparian forests. Perhaps the primary threat of
grazing is to the low-elevation riparian forests.
These forests may represent critical linkages
among the mountain ranges. Modified and
degraded riparian forests may inhibit dispersal

among mountain ranges and gene flow among
owl subpopulations.
Land ownership within the Basin and Range
- West is a mosaic of public and private lands
(II.B). Most major mountain ranges fall under
Federal jurisdiction, with some private
inholdings and other lands administered by the
San Carlos Apache and White Mountain Apache
tribes. Much of the shrublands and grasslands
between mountain ranges are administered by
the FS or BLM, but a fair portion is privately
owned. Many of these private lands are used for
cattle, which graze both in upland and adjoining
riparian communities. Grazing in riparian
communities is a concern because of the potential
for negative impacts on areas that can provide
dispersal habitat among mountain ranges.
This mosaic pattern of jurisdiction by multiple
landholders may impede coordinated management
efforts for the owl.
Most land development within the RU is
related to enhancing recreation opportunities.
These include developing or expanding campgrounds
(e.g., Twilight Campground in the
Pinaleno Mountains, the loop turn at John
Hand Lake in the Chiricahuas) or enlarging
roads for safety (e.g., widening of Mount
Lemmon highway in the Santa Catalina Mountains).
Developments such as these often require
removing trees, potentially altering owl habitat.
Further, a rapidly increasing human population
in the southwest portends increasing urban
development which can potentially encroach
upon owl habitat and also impact groundwater
regimes, potentially impacting riparian systems.
Evergreen oak and pinyon-juniper woodlands
receive the most pressure from fuelwood
harvest. Historical harvest of mature mesquite
stands within the shrubland and grassland areas
may have contributed to the demise of the
riparian forest, thus continued harvest of mature
mesquite in these areas may be a concern.
Basin Basin Basin and and and Range Range Range - - - East East
East
The Basin and Range - East RU lies mostly
within New Mexico and supports the second
largest known number of Mexican spotted owls
in the United States. It adjoins four U.S. and
one Mexican RUs. Mexican spotted owls occur-
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ring in the Sacramento Mountains have been
exposed to various disturbances for more than a
century. Natural disturbances include forest fires
plus insect and disease outbreaks. Human
disturbances include timber and fuelwood
harvest, grazing, land development, and recreation.
The cumulative effects of these natural
and anthropogenic disturbances have resulted in
a landscape that differs from that existing prior
to European settlement. The threat of these
disturbances to the owl’s persistence cannot be
quantified at this time, but certain incongruities
are detectable. For example, owl density is
relatively high on FS lands, but fecundity is
quite variable over time and annual survival is
unknown. Thus, even though the current
population density may be high, we know
nothing of population trends. Further, given
existing forest conditions in this RU, threats of
widescale habitat loss are real and immediate.
Consequently, active management is needed to
alleviate these threats while ensuring that adequate
habitat will exist well into the future.
Potential Potential Threats
Threats
The Team categorized potential threats to
spotted owl recovery according to magnitude.
Major threats pose immediate potential for
causing declines in spotted owl populations, and
minor threats present no such immediacy. Major
threats, in order of potential effects, include (1)
catastrophic, stand-replacement fires, (2) some
forms of timber harvest, (3) fuelwood harvest,
(4) grazing, (5) agriculture or development for
human habitation, and (6) forest insects and
disease. Minor threats are activities not currently
extensive in time or space but that have been
considered potential threats to the owl. These
include (1) certain military operations, (2) other
habitat alterations (e.g. power line and road
construction, noxious weed control), (3) mining,
and (4) recreation.
Existing dense forest conditions makes much
of the Basin and Range - East RU vulnerable to
catastrophic fire. Such stand-replacing fires have
been documented in the Sacramento Mountains
since the 1950s and continue to the present
(e.g., the Burgett and Bridge fires in 1993 and
1994, respectively). Similar fires occurred in the

Smokey Bear Ranger District (Hanks and Dick-
Peddie 1974) and other mountain ranges in the
Basin and Range - East RU (Plummer and
Gowsell 1904, Moody et al. 1992). Failure to
address this potential for fire by reducing fuel
levels and fuel continuity will inevitably lead to
more and larger fires resulting in the continued
loss of owl habitat.
Past timber harvest practices have left a few
remnant old-growth stands and residual pockets
of pre-harvest trees in the Sacramento Mountains.
Trees older than 200 ybh (years at breast
height) can be found in these remnant stands
and pockets. Many of these stands, however, are
small (

indicates that spotted owls use forest types not
typically found in the United States and that
land-management practices differ substantially
in Mexico from those in the U.S. The Team
proposes that the general recommendations be
applied within the Mexican RUs where appropriate.
The Team strongly recommends that RU
working teams (see Part IV) develop management
recommendations for Mexico more fully.
The Mexican spotted owl is typically found
in montane habitats where the vegetation is
dominated by pines and oaks. Although spotted
owls in the U.S. also use pine-oak forests, they
vary somewhat in composition and structure
from similar forests in Mexico. However, within
Mexican pine-oak forests, spotted owls appear to
favor canyons, as they do in many of the areas
used in the U.S.
Because social and economic systems in
Mexico differ from those in the U.S., activities
that take place within potential spotted owl
habitat differ somewhat between the two countries.
Whereas grazing, fire, timber harvest, and
fuelwood harvest are threats common to both
countries, other threats are unique to Mexico
and some to specific RUs.
Potential Potential Threats
Threats
Sierra Sierra Madre Madre Occidental Occidental - - Norte Norte.— Norte .— .—The .— primary
threat is land conversion for subsistence
agriculture. Impacts of this threat include the
loss of spotted owl habitat, soil loss, and erosion.
A related threat is overgrazing by livestock.
Historically and through the present, forest
lands have been cleared to create pastures for
cattle; the cumulative effects of these practices
have modified spotted owl habitat. Although
extensive timber harvest occurs within this RU,
most harvest occurs in the uplands and is not a
direct threat to spotted owls found in canyons.
Whether or not timber harvest indirectly affects
the owl is unknown, but could be a concern
worth addressing through research.
Sierra Sierra Sierra Madre Madre Oriental Oriental - - Norte Norte.— Norte .— .—Timber .—
harvest and grazing are the primary threats
within this RU. The main effects of these threats
is to further fragment an already disjunct population.
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Sierra Sierra Madre Madre Occidental Occidental - - Sur Sur.— Sur .— .—Primary .—
threats within this RU are fuelwood harvest,
timber harvest, charcoal production, grazing,
and agricultural development. Fuelwood harvest
often entails cutting snags and the harvest of
riparian plant species, both of which are critical
components of spotted owl habitat. Timber
harvest in itself is not a direct threat to spotted
owl habitat. However, harvest methods that
entail rolling logs from higher to lower sites
result in soil loss and erosion, thereby affecting
the habitat of the owl and its prey. Fire is considered
only a moderate threat because of the
disjunct distribution of owls in canyons and
because limited efforts towards fire suppression
have allowed natural fire regimes to persist. Fire,
however, can possibly destroy spotted owl
habitat under the right conditions. Livestock
graze throughout the year within spotted owl
habitat, and the cumulative effect of this grazing
affects prey habitat and spotted owl habitat
structure. Type conversion of forests for agriculture
also occurs within this RU.
Sierra Sierra Madre Madre Oriental Oriental Oriental - - - Sur Sur.— Sur .— .—The .— potential
threats in this RU parallel those within Sierra
Madre Occidental - Norte RU. The primary
difference is that this RU probably contains the
best and most extensive habitat within any of the
Mexican RUs, thus threats can occur over a
much greater area.
Eje Eje Neovolcanico
Neovolcanico.—
Neovolcanico .— .—The .— primary threats in this
RU are those associated with population expansion
and industrial development. Specifically,
industrial development can lead to loss of habitat
and an increase in pollution. Other threats
include management to control insects and
disease, fire suppression, grazing, and agricultural
development.

The Team has assimilated, reviewed, and
analyzed data generated by the Mexican Spotted
Owl Monitoring Program of FS Region 3. We
have also compiled and reviewed data from the
BLM and the FS Region 4 in Utah, and FS
Region 2 in Colorado. Here, we offer an alternative
design for monitoring the Mexican spotted
owl population within the three core RUs. We
also provide recommendations for monitoring
habitat throughout the owl’s range. This proposed
monitoring program will evaluate population
and habitat trends as required by the criteria
for delisting the species (III.A). The philosophy
of our proposed monitoring scheme is to measure
the critical variables--changes in owl numbers
and changes in habitat--needed for delisting
the species.
For the purposes of recovery and understanding
effects of land management activities
on the Mexican spotted owl, monitoring should
determine with adequate reliability temporal
changes in the owl population and its habitat
when in fact such changes are occurring. An
effective monitoring program requires measuring
changes in habitat quantity, estimating population
size of territorial owls, and determining key
demographic parameters including survival,
recruitment, and reproduction, all of which
influence population size.
Habitat monitoring will rely heavily on both
remote-sensing of habitat across the range of the
bird and field measurements of habitat variables
before and after treatments. Population monitoring
is based on mark-recapture theory and
Cormack-Jolly-Seber modeling approaches,
similar to Pollock’s robust design approach
(Lefebre et al. 1982, Pollock 1982, Kendall and
Pollock 1992). To our knowledge, a systematic
habitat monitoring approach as extensive and
intensive as the one we propose has never been
implemented. In contrast, a prototype design for
population monitoring was implemented in
Olympic National Park, Washington (Noon et
al. 1993, E. Seamen pers. comm.) to monitor a
northern spotted owl population.
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Mexican Spotted Owl Recovery Plan
Accurate and efficient protocols for both
habitat and population monitoring require pilot
studies to estimate recapture probabilities, and to
estimate variances associated with each of the
population parameters and each of the habitat
variables. For population monitoring, these
estimates can then be used to determine optimal
quadrat size and numbers of quadrats required
within predefined strata and RUs. Funding was
allocated in 1994 to further refine the proposed
population design with a small field trial involving
four quadrats. Results of this field trial
validated the study design provided qualified
personnel conduct the work (May et al., in
press). A larger pilot study is needed to refine
parameter estimates for actual implementation
of the proposed design. For habitat monitoring,
separate pilot studies will be needed to establish
sampling designs, including sample size requirements.
HABITAT HABITAT MONITORING
MONITORING
The habitat delisting criterion states that
habitat monitoring must be implemented (1) to
track changes in the quantity of macrohabitat
and (2) to verify that microhabitat changes
within treated stands meet the intent of the
Recovery Plan. Thus little, if any, owl habitat can
be lost if this goal is to be met. Further, habitat
quality cannot decline significantly. A concern of
the Team is that habitat quality cannot be
adequately assessed, particularly with remotesensing
data. To alleviate this concern, our
recommendations also include field measurements
of microhabitat characteristics within
treated stands. However, we reiterate that
macrohabitat quantity should also be monitored
on a rangewide basis.
Macrohabitat
Macrohabitat
Macrohabitat
The purpose of rangewide monitoring is to
track gross changes in habitat as the result of
disturbance, from both natural (e.g., fire) and

anthropogenic (e.g., timber harvest, prescribed
fire) causes. Given the extent of the area to be
monitored, remote-sensing technology will be
required. An imagery baseline should be established
within six months of Recovery Plan
approval using LANDSAT Thematic Mapper
imagery (currently available in the FS Region 3
Geometronics Remote-Sensing Laboratory). The
imagery for potential owl habitat and surrounding
areas should be aggregated, georeferenced,
and merged with vector map data to provide
image maps. These image maps may be used
both as general planning tools and as a baseline
for detecting change. The 30-m (98-ft) spatial
resolution of the LANDSAT Thematic Mapper
imagery is adequate to detect both anthropogenic
and natural change across large land areas.
Changes that can be detected include wildfire
scars, timber harvests, gross changes in forest
health, and possibly the addition or removal of
roads, large developments and other cultural
features, and fluctuations in grazing practices.
In a standard change-detection analysis, two
image data sets are co-registered and then subtracted
from each other. The resulting difference
image highlights changes across the area covered
by the image data sets. An additional image data
set will need to be purchased in the future to
perform change detection. The additional data
set may be either LANDSAT Thematic Mapper
(TM) data or LANDSAT Multispectral Scanner
(MSS) data. A TM data set would be preferred,
but MSS data could be substituted and would
provide adequate spectral and spatial resolution
to perform useful change detection.
The baseline TM data set can also be used to
develop a generalized regional vegetation cover
map, using standard supervised and unsupervised
image classification techniques with TM
bands 4, 3, and 2. The literature indicates that
the 4,3,2 band combination is most useful for
vegetation analysis. Developing a vegetation map
would also require the integration of 1:250,000
digital elevation data to account for the effects of
varying slope aspects and elevation on vegetation
patterns.
Texture analysis techniques may be used to
assess vegetation structure and density across
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large areas using either the LANDSAT TM or
MSS data. While texture analysis applications in
vegetation analysis have appeared frequently in
the literature, the methodologies are not as
widely accepted as image classification techniques,
so they must be considered experimental.
Given the resolution possible with the tools
and information available, remote sensing
monitoring techniques will provide an estimate
of macrohabitat trend. Within five years of
creating the imagery baseline, participating
agencies should produce a report assessing
changes in vegetation composition, structure,
and density. This will provide an interim checkpoint
to determine if the delisting criteria can be
met at the end of 10 years.
Microhabitat
Microhabitat
Microhabitat monitoring is required because
remote sensing is largely insensitive to subtle
intra-stand changes that may enhance or degrade
owl habitat. Microhabitat monitoring will entail
measuring habitat variables before and after
silvicultural or prescribed fire treatments designed
to maintain, improve, or create owl
habitat. This monitoring is to verify that treatments
(silviculture, fire) are meeting their stated
objectives. We acknowledge that many treated
stands will not meet the desired future condition
in 10 years, but the trajectory on which a stand
is placed can be modeled to evaluate if it is
moving towards owl habitat. This knowledge is
needed to demonstrate that any short-term losses
in macrohabitat will be partially offset as stands
mature into owl habitat. If adequate acreage of
vegetation is moving towards owl habitat, our
confidence in long-term habitat stability will
be enhanced.
Sampling units will be treated stands. Within
these stands, an adequate number of vegetation
sampling points must be established. The exact
number of sampling points needed will be
dictated by the most variable characteristic
(likely snag density; Bull et al. 1990). Points
should be sampled prior to initiating a treatment,
resampled following the treatment after
allowing adequate time for the area to equilibrate

from temporary disturbance effects, and then at
five-year intervals. The variables measured can
then be input into a vegetation model to estimate
stand characteristics at different points in
time.
At a minimum the following variables
should be measured and assessed: (1) tree diameters
by species, (2) tree basal area by species, (3)
size-class distributions of trees, (4) log volume by
size class, (5) canopy cover, (6) snag diameter,
and (7) snag basal area. We strongly advocate
that additional variables be included that might
be relevant to monitoring other ecosystem
attributes. The return in critical monitoring
information derived by expanding the variables
measured would far outweigh any additional
costs, assuming that the new variables are not
highly correlated with the variables suggested
above.
POPULATION POPULATION MONITORING
MONITORING
Monitoring habitat as a singular effort will
not adequately reveal the true status of the owl
population. Relatively long-lived birds with a
high (~0.89) adult survival, Mexican spotted
owls may live 16 years or more once they reach
adulthood. However, an intense period of
mortality during the first year could produce
population consequences that habitat monitoring
would not detect. Habitat quality could
decline from various natural processes or anthropogenic
activities, yet the territorial population
would remain unchanged because of site fidelity
among existing birds and recruitment of floaters.
Young might still be produced, but would not
survive to be recruited into the territorial population
because of poor habitat quality, limited
habitat availability, or because their inexperience
would not allow them to survive and disperse
during their first year.
A limitation of this proposed monitoring
scheme (and all known approaches) is that only
territorial birds are monitored. The total or
proportional number of floaters (sensu Franklin
1992) remains undetermined and unmonitored
relative to the target population.
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Because nonterritorial birds are not directly
monitored, we want to guard against an undetected
decline in the total population of spotted
owls when the territorial population remains
stable. We suggest the following procedures to
evaluate trends in the nonterritorial population.
First, the age of birds that establish territories
will indicate the size of the nonterritorial population.
If new territorial birds are only one year
old, then they have never existed as floaters in
the population. Thus, a decline in the age of
territorial birds suggests that the nonterritorial
population is low or declining (Franklin 1992).
Second, the presence of unfilled territories would
suggest that an inadequate floater population
exists, and hence that a decline in the population
is taking place.
In the following, we outline a suitable
framework and statistical estimation approach
for monitoring owl populations in 3 RUs.
However, critical design and sampling details,
such as sample sizes and delineation of strata,
have been omitted, and must be developed by an
implementation team as data become available
to make those decisions.
Target Target Population
Population
The target population for the abundance
estimate is territorial Mexican spotted owls
(exclusive of floaters) in the Upper Gila Mountains,
Basin and Range - West, and Basin and
Range - East RUs. Thus, all potential owl habitat
in these 3 RUs must be included in the sampling
frame. All land management jurisdictions are
encouraged to cooperate in providing access and
resources to monitor the entire owl population.
Sampling Sampling Units
Units
Sampling units will consist of 50 to 75 km 2
(19 to 29 mi 2 ) quadrats randomly allocated to
habitat strata. Quadrats will be defined based on
ecological boundaries such as ridge lines and
watersheds to reduce edge effects. Selection of
quadrat boundaries must emphasize edges that
are unlikely to traverse owl territories, so that the
errors of including a territory in multiple quad-

ats or in no quadrat do not occur. The exact
number of quadrats and their size will depend
on the specifics of implementing the monitoring
scheme and results of pilot studies.
In general, the population monitoring
scheme will require: (1) determining strata that
represent different owl densities or habitat types
occupied by owls within each RU; (2) determining
quadrat size which should be sufficiently
large to reduce edge effects and small enough to
allow a minimum of four surveys per quadrat in
the survey season limited to 1 April to 30 August
(initial approximation of quadrat size is 50 to
75 km 2 [19 to 29 mi 2 ] [May et al., in press]);
(3) defining the sampling frame of quadrats in
each stratum such that quadrats are relatively
equal in size and have boundaries selected to
minimize edge effect; (4) selecting a random
sample of quadrats from each stratum the first
year, and then randomly replacing 20% of the
sampled quadrats each year with quadrats
randomly selected from the currently unsampled
quadrats (with quadrats in the initial sample
potentially removed, and then possibly included
in the sample again at a later time); and (5)
developing protocols for conducting field
surveys (likely different from past FS protocols
because of the different goal of the proposed
procedure from past goals).
Sampling Sampling Procedures
Procedures
Stratification
Stratification
LANDSAT multispectral scanner imagery
with 30-m spatial resolution would be suitable
for defining habitat strata within each RU, and
thus the sampling frame of quadrats for each
stratum. Approximate density of territorial owls
within strata can then be used to allocate survey
effort (number of quadrats) to strata. The
optimum allocation of survey effort is one that
would minimize erroneous estimation of spotted
owl abundance. Optimal allocation of quadrats
to strata will probably not be in proportion to
strata size. More likely, optimal allocation will
mean that a higher percentage of quadrats in
strata with high owl densities will be sampled.
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Optimal allocation might also take into account
the cost per quadrat because of potential differences
in the cost of measuring quadrats within
different strata. Strata should be computed both
as projected (ignoring topography) and as
surface (incorporating topography) areas because
differences in topography affect vegetation type.
Selection Selection of of Quadrats
Quadrats
Within strata, quadrats will be randomly
selected for inclusion in the sample. We suggest
that 80% (randomly selected) of the previous
year’s quadrats be revisited the following year.
The other 20% of the previous year’s quadrats
should be removed from the sample, and a
replacement sample of quadrats not sampled the
previous year should be substituted. Quadrats
removed one year can included in the sample in
following years provided that it is randomly
selected and that at least one year has elapsed
since it was last sampled. This procedure means
that the average number of years that a particular
quadrat remains in the sample is 4.5 years.
Inclusion of new quadrats into the sample each
year guards against management practices within
the sampled quadrats not being representative of
those practices occurring elsewhere. This rotation
of quadrats included in the sample will
provide a smaller variance because observations
are correlated across time and many quadrats will
be sampled repeatedly, but still provides a
representative sample of the available quadrats.
Sampling Sampling Within Within Quadrats
Quadrats
Sampling procedures within a quadrat will
include (1) assigning survey stations to ensure
adequate coverage and a standardized density of
such stations among quadrats; (2) allowing for a
minimum of four complete (i.e., all call points
sampled) surveys through each quadrat; (3)
conducting nighttime surveys from survey
stations to map general locations of spotted owls
and to estimate per-visit detection probabilities;
and (4) conducting daytime (auxiliary) surveys
and mousing to find roosting and nesting
spotted owls, determine if a mate not detected

during nighttime survey is present, determine
number of young present, and capture and
color-mark all spotted owls found. For each
spotted owl found, the center of its activity area
must be determined as either in or out of the
quadrat.
Proper timing of surveys maximizes efficiency
in locating spotted owls. We recommend
that nighttime surveys be conducted within 3
hours following sunset. Owls detected at dusk
are near diurnal roosts and thus provide an
optimal starting point for confirming pairs and
reproduction during daytime surveys. Similarly,
daytime surveys should begin at or near sunrise
(preferably just before) as owls are returning to
their roosts.
Banding Banding Banding Birds
Birds
Marking individual birds with FWS leg
bands and color bands for visual identification
provides greater validity in the estimation of the
owl population size on the quadrat because the
assumptions of the mark-recapture methods can
be tested. Conceivably, owl population size on
quadrats with high densities of owls might be
underestimated without banding because two
different birds might be counted as only one.
Conversely, on quadrats with low densities, a
single bird might be counted as 2 birds, biasing
the population estimate high. Individually
marking birds will eliminate some of this potential
bias. Second, banding birds is necessary to
estimate annual survival on quadrats that are
sampled for two consecutive years. Third,
capturing birds allows more careful aging of
individuals; hence, the resulting age structure
data are more useful in assessing the impact of
floaters in the population. Finally, minimum
estimates of dispersal and emigration from the
quadrat can be assessed with banded birds that
are located off the quadrat. Although the cost of
the population estimation procedure may be
increased by up to 40% by individually marking
birds (May et al., in press), the Team feels the
additional information and rigor provided by
marking birds is justified.
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Statistical Statistical Analysis
Analysis
Mexican Spotted Owl Recovery Plan
Noon et al. (1993) provide the following
statistical discussion.
Estimation Estimation of of of Capture Capture Probability Probability
Probability
The described spotted owl surveys will
provide data regarding the number of territorial
owls detected and determined to have their
activity centers within the survey plots. It is
unlikely that all owls with activity foci lying
within these plots will be detected, and capture
probabilities will therefore be less than 1. Capture
is defined as either physically capturing and
uniquely marking an individual or resighting its
unique color band combination without physically
recapturing it. Thus, the per-visit capture
probabilities must be estimated to “correct” the
count statistics and reflect the true number of
territorial birds with activity centers within
quadrat boundaries.
Per-visit capture probabilities can be estimated
using data on the capture histories of
individual owls on the quadrats. The four
surveys will be conducted during a relatively
short period, so it is appropriate to use capturerecapture
models for closed populations (e.g.,
Otis et al. 1978, White et al. 1982, Pollock et al.
1990). Per-visit capture probabilities may vary by
visits, strata, RUs, and years. However, substantial
gains in the precision of capture probability
estimates would be achieved if they could be
estimated using data pooled over visits, strata,
RUs, or years. Standardized survey protocol
within and among quadrats using field crews
with communal training should decrease the
variation in per-visit capture probabilities.
Heterogeneity of per-visit capture probabilities
across individuals should be examined. If
heterogeneity is found, estimators developed
under model M h of Otis et al. (1978), such as
the jackknife (Burnham and Overton 1978,
1979) and Chao’s (1987, 1988, 1989) estimator
are appropriate. If heterogeneity is not serious,
models with data pooled over visits, strata, RUs,
and years should be considered.
Capture probability estimates resulting from
these modeling efforts will pertain to the prob

ability of detecting and capturing an individual
spotted owl during a single survey visit. Capture
history data, and hence the capture probability
estimates, will be restricted to those spotted owls
with a nest or focus of activity within the area
being sampled. The density estimation procedure
(see below) actually requires an estimate of
the probability of detecting and capturing a
spotted owl at least once during an entire season.
Given owl presence, the estimated probability of
detecting and capturing an owl during the
season using surveys is given by
Volume I/Part III
p = 1 - (1 - p) k k ^
,
where p k is the probability of detecting and
capturing a spotted owl at least once during
k visits, and p is the single-visit capture probability.
The above scheme for estimating capture
probability should work well with owls initially
detected from survey points within the quadrat.
However, these capture probabilities are not
applicable, by themselves, to other pair members
found during daytime visits or to spotted owls
located other than by calling from survey points.
To include data from pair members located
during daytime visits, we consider their capture
probability as the product of the probability of
capturing a pair member from survey points
times the probability of capturing the other pair
member during a daytime visit given capture of
one mate from survey points. The first probability
in this product is obtained using capture
histories (i.e., capture probabilities) of birds
detected from survey points as previously described.
The second, conditional probability
must be obtained using data from daytime visits
and captures only.
Auxiliary or daytime visits can be viewed in
the context of removal modeling (e.g., Zippin
1956, 1958; Otis et al. 1978; Ward et al. 1991).
The primary purpose of daytime visits is to
determine pair and breeding status of birds
detected from survey points. Auxiliary visits may
or may not be terminated after capture of the
mate, depending on whether data on reproductive
success is adequately obtained.
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Mexican Spotted Owl Recovery Plan
Estimation Estimation Estimation of of of Density Density Per Per Quadrat
Quadrat
Each quadrat requires two parts to the
estimation process. First, estimation of apparent
density by
^
Di n n· + n¨ a i i i
= = ,
which is the total number of spotted owls
detected and having activity centers in quadrat i
·
¨
(n i ), based on both survey (n i ) and auxiliary (n i )
visits divided by the area of the quadrat (a i ).
Next, apparent density is adjusted for those
spotted owls that maintain an activity center
within the quadrat but were not detected during
a survey visit. The adjustment for the survey visit
is the reciprocal of p , the probability of a
k
spotted owl being captured at least once on a
given survey based on k visits to quadrat i. Note
that p pertains only to the n animals detected
k i
during the survey point visits of quadrat i, not to
birds detected on auxiliary visits. If auxiliary
visits are made to determine pair or reproductive
status, any additional pair members that are
detected contribute to the density estimate for
quadrat i. As discussed previously, their capture
is conditional upon an initial capture from a
survey point. To adjust the count of the n owls i
detected on quadrat i during auxiliary visits, we
divide the count by the probability of detecting a
pair member during k auxiliary visits (p ), given
k
detection and capture of its mate from survey
points. Thus, we would estimate density on
quadrat i as
ni ^ p^ D = k .
i + ni ¨
^
^
·
¨
¨
·
p^ p¨ k k
Estimation Estimation of of Density Density Per Per Stratum
Stratum
Once we have density estimates for each
quadrat within a stratum, they can be combined
into an overall mean estimate of density for the
stratum. Because quadrats are not the same size,
weighting of the quadrat density estimates by
area is essential, so that
D j =
m j
S
a i
a i
^
a D i=1 i i ,
mj Sai
i=1
a i

where m is the number of quadrats in stratum j.
j
To obtain population size estimates for each
stratum (j), multiply by the area of the stratum
^
(A ) so that N = D · A . Note that A may change
j j j j j
through time as habitat changes and quadrats are
moved from one stratum to another.
An estimate of overall abundance for RU u is
mu ^ ^
then N = S N , where m is the number of
u j=1 j u
strata in RU u.
Variance Variance Estimators
Estimators
With stratified-random sampling, we usually
have simple variance equations because the
stratum means of totals are independent between
strata. Here, this is not the case because corrections
for spotted owls not seen are common
across strata and induce the need for covariance
terms. These variance equations will need to be
developed. Specific closed-formed solutions may
not be possible for the variance estimates. Thus,
estimating the variance components by bootstrap
methods may be more feasible.
Cormack-Jolly-Seber Cormack-Jolly-Seber Models
Models
Cormack-Jolly-Seber (CJS) models
(Lebreton et al. 1992) can be used to estimate
age-specific apparent survival (f a ) and recruitment
to the territorial population (B). We
suggest using CJS modeling procedures as
outlined by Lebreton et al. (1992), Burnham
and Anderson (1992), Pollock et al. (1990), and
Burnham et al. (1987). This approach is demonstrated
by White et al. (1995) for the analysis of
data from the demographic study areas. We
suggest that data from all quadrats within a
stratum (or even larger area) can be pooled to
estimate apparent survival and recruitment.
Both the apparent survival (f) and recruitment
(B) are biased estimates of true survival (S)
and true recruitment rates because the quadrats
do not have geographic closure. For survival,
f = S - E, where E is the emigration rate off the
quadrats. For recruitment, B = R + I, where R is
true recruitment and I is immigration onto the
quadrats. If the area of the combined quadrats
were used in a single demographic study area,
the bias of f and B would be smaller because the
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probability of birds emigrating off of and immigrating
onto a large single area would be smaller
than for a collection of small quadrats representing
the same area. However, if we assume that
this bias is somewhat constant across time, then
tests for changes in f and B across time with
models such as f T as demonstrated by Burnham
et al. (1994) provide a potent tool to assess
changes in these population parameters through
time. The optimal size of quadrats is dictated by
keeping them large enough that reasonable
estimates of the number of territorial birds
present can be accomplished, while small
enough so that an adequately large sample of
quadrats is possible to estimate precisely the
among-quadrat variation.
We would not suggest that f and B be used
to compute l in a Leslie matrix model as was
done with the demographic study areas by
White et al. (1995). Biases caused by emigration
and immigration make any estimate of l computed
from these parameters biased as well.
Furthermore, the main objective of the quadrat
surveys is to provide an unbiased estimate of the
total number of territorial owls so that an
unbiased estimate of l can be obtained as
^ ^ ^
l = N t+1 /N t .
Estimates of juvenile apparent survival
obtained from the CJS model with banding data
from juvenile spotted owls will probably not be
useful from the pooled quadrat survey data
because the emigration rate of this population
segment will be quite high as they disperse away
from their natal territories.
Personnel Personnel
Personnel
Quality work cannot be completed without
capable people who desire to perform well. Owl
surveys are difficult to conduct. To achieve
accurate survey results requires a certain combination
of physical and mental traits. The ideal
candidate for spotted owl survey work must be
physically capable of negotiating difficult terrain
and doing so after dark. The mental demands
include the intellectual capacity to understand
the nuances of the work, the perseverance to
succeed under adverse conditions, the ability to
follow directions, and the discipline to be

patient. Rigorous training to certify people to
conduct monitoring is a critical step to ensure
that qualified people implement the procedures.
Restrictions on duration of work day, night
time work, and camping near survey sites can
lead to inefficiency. Effective inventory and
monitoring may often require personnel to
survey between dusk and 2300 hrs and prior to
sunrise the next morning if an owl is detected
the previous night. Not permitting camping at
sites or not allowing more than 8-hour work
days is an ineffective survey strategy. Thus, cost
and effort for determining occupancy or reproduction
in a given territory may be doubled or
tripled. Not allowing personnel to survey along
marked ridge lines at night (i.e., off roads) may
result in inadequate survey of an area. Competent,
qualified, eager personnel can conduct such
activities safely and with desired results as demonstrated
by May et al. (in press).
Training
Training
Training is the most important mechanism
for ensuring quality data and standardization.
The current certification program employed by
the FS should continue, but in a more intense
fashion. High-quality photographic media,
including video tapes of proper procedures,
should be incorporated. Use of a map, compass,
and GPS system, and recording spatial information
with Universal Transverse Mercator (UTM)
coordinates (Grubb and Eakle 1988) are critical.
Additional training for recording information on
data forms, maps, and in an electronic data base
is required (see below). Certified owl biologists
should be tested routinely on their ability to
complete data forms and plot locations correctly.
A standardized procedure for storing all information
also needs to be developed and enforced.
All training must be reinforced with adequate
(4-day minimum) field exercises followed
by periodic reinforcement of learned skills.
Although initial skills may be provided with the
certification process, reinforcement through
feedback on procedures and results is required.
An electronic data entry program will help to
standardize inputs and reinforce proper documentation
procedures. Such a routine will also
indicate progress of the monitoring program and
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identify personnel or administrative units that
need additional training. Further, additional
training should include periodic visits by program
supervisors to review field procedures.
Incorrect observations may not necessarily be
detected on data forms.
We also suggest a greater emphasis on
identification of spotted owl age classes (juvenile,
subadult, and adult) as described by Forsman
(1981) and Moen et al. (1991). This valuable
information may be obtained if observers take
binoculars on surveys. Information on age
structure may prove useful for identifying
changes in demographic trends.
All survey routes and results need to be
summarized in a standardized manner on media
that can be entered into a Geographic Information
System (GIS). Thus, field personnel will
require training on use of map, compass, and
GPS. In addition, a standardized map system
and symbol set is paramount. We recommend a
7.5" USGS topographic map. This map type is
readily available in paper and digital form. We
also insist that field personnel record UTM
coordinates. This will allow rapid updating of
digital maps of owl locations.
Computerized Computerized Data Data Data Entry Entry and and
and
Summarization
Summarization
A major weakness of past inventory and
monitoring programs has been the lack of
accessibility to data; as a result, few summaries
and analyses were prepared. This scarcity of data
examination appears to be due to the lack of a
central, accessible, computerized database where
field forms are regularly entered for computer
analysis. Field workers submitting data forms but
not receiving feedback from their efforts nor a
copy of the master database for them to review
leads to errors that are difficult to rectify retroactively.
We suggest that field workers who collect
the data should also be responsible for data entry
into a standardized computer form. The benefits
would be twofold.
First, a computerized data entry form would
guarantee that only admissible codes are used
because invalid codes would not be accepted by
the computer, and correct entries would be

needed in all data fields before the user could
proceed. Quality control would be facilitated via
an interactive computer data entry interface.
With such a data entry program, data from
different jurisdictions of all involved land management
entities would be compatible.
Second, once the data have been entered,
summaries can be produced with standard
summary programs. At a minimum, field workers
should be able to produce summaries of data
they entered, and make comparisons with past
years and maybe other geographic areas. The
main reason for this instant feedback is to
encourage field personnel to examine their own
data plus get a temporal and spatial perspective
of existing data. Field workers would have a
much better picture of how their data fit into the
overall effort and would have access to data in
the master database. Simple graphs and tabular
summaries should be available via a menu
system. This feedback would also promote
greater cooperation in future surveys and makes
the field worker feel a part of the complete
process.
Creation of a master database on an accessible
computer network (such as the World Wide
Web [WWW] on Internet) has another, less
apparent, benefit for the program. From this
master database, region-wide summaries could
be generated. Annual summaries would help
detect trends in the data. Sophisticated statistical
analyses could be programmed to implement
tests for trends in the data. Safeguards would be
necessary to limit access to the data, particularly
sensitive site locations, to only authorized
persons. Finally, scrutiny by outside reviewers
would improve the integrity of the database.
To implement the above scheme, two pieces
of software need to be written. The first is the
data entry system, for which extensive error
checking should be coded into the software.
Data entered by a field worker would be appended
to the master data file only after passing
a stringent series of integrity checks. The second
is a data summary program that would be menu
driven and allow the user to summarize his/her
own data plus other data of interest. We presume
that modern PC computer software systems and
access to a computer network should make this
software development fairly easy. Once the field
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season is completed, each land management
entity and their respective subunits should be
able to obtain graphical summaries as well as
statistical summaries in tabular form.
Costs
Costs
The cost for implementing the population
monitoring scheme should include hiring a
principal investigator to design this survey and
coordinate sampling efforts. Field crew leaders
will be necessary for supervising study logistics
and field technicians will be required to conduct
surveys. In addition, while models exist for
estimating total population size through time,
models of multiple capture probabilities require
some independent work. All field personnel
hired to conduct the pilot study and subsequent
monitoring program must be qualified and
trained.
Our initial estimate of the costs to fully
implement the proposed monitoring scheme is
approximately $1.2-1.5 million per year. Based
on the delisting criteria, monitoring must
continue for a minimum of 15 years.
Costs for implementing macrohabitat
monitoring are unknown. However, much of the
needed remote-sensing coverage exists or is being
obtained as a tool for implementing ecosystem
management. Thus, additional costs attributable
to the spotted owl should be minimal. Costs of
implementing microhabitat sampling are difficult
to estimate without knowledge of the
number of plots to be sampled. We assume,
however, that sampling an area pre- and posttreatment
is already required as a standard part
of activity implementation; consequently, the
cost attributable to owl monitoring would entail
those associated with measuring additional
variables specific to the owl. Thus, the total costs
of habitat monitoring should be relatively
minimal beyond that already required or in the
process of being developed independent of the
spotted owl.
Potential Potential Experiments
Experiments
Many habitat variables important to Mexican
spotted owls cannot be monitored by remote
sensing. Further, it is important to ensure that

adequate habitat is provided for key prey as well.
Thus, we propose some potential experiments to
relate habitat conditions to owl population
dynamics where key habitat characteristics would
be measured on the ground. On-the-ground
monitoring of relevant habitat characteristics
would quantify their change at a local (i.e.,
within quadrat) scale and relate them to owl
population dynamics.
Population monitoring based on randomly
selected quadrats provides the opportunity to
conduct experiments to extend our knowledge of
the impact of habitat manipulation on Mexican
spotted owl population dynamics. We propose
these experiments to produce credible, defensible,
and reliable results (sensu Murphy and
Noon 1991). Quadrats within the monitoring
design may serve as experimental units for
examining the effects of future management
such as fires, grazing, timber harvest, and recreation.
Given that a treatment is identified prior to
its occurrence, vegetation measurements can take
place on the site of the expected treatment and a
second, control quadrat that is selected based on
its similarity to the expected treatment quadrat.
This experimental design is not a true experiment,
because the treatment is not randomly
allocated to one of the pair of quadrats. However,
this quasi-experiment is still more powerful
in developing cause-and-effect relationships
between habitat manipulations and owl population
dynamics than the more common correlative
designs used by past researchers (see III.D
for further details on experimental design).
Further, the capability to replicate the treatment
exists because of the extensive number of quadrats
that will be required for measuring changes
in population size.
Areas where planned treatments result in
some form of habitat alteration provide excellent
opportunities for quasi-experiments. Vegetation
measures should be taken immediately before
and after the habitat-modifying event, and
thereafter at 5-year intervals. Vegetation measurements
that seem especially important to
examine are tree size-class distribution, log sizeclass
distribution, canopy cover, and shrub cover.
Results from these experiments, coupled with
results of population monitoring, will provide
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the basis for a predictive model of spotted owl
habitat quality (assuming that owl density
reflects habitat quality). Data on apparent owl
survival and reproduction will also be available,
which may relate to habitat quality more directly
than owl density.
Alternative Alternative Designs Designs Designs for for Population
Population
Monitoring
Monitoring
Drawing Drawing New New Sample Sample of of Quadrats Quadrats Quadrats Each Each Each Year
Year
Instead of drawing an initial sample of
quadrats from the sampling frame and monitoring
these same quadrats through time, an alternative
approach would be to draw a completely
new random sample of quadrats each year. For
repeated sampling of a set of quadrats to be
legitimate, normal activities that occur in spotted
owl habitat should continue during the
monitoring program, provided these activities
meet the requirements of section 7(a)(2) of the
Act by not likely jeopardizing the continued
existence of the Mexican spotted owl. The main
advantage of a new sample each year is that it
guards against the potential for land managers to
manage areas within the quadrats differently
than the remainder of the landscape. The price
of this protection is relatively great as illustrated
by these four points: (1) the logistics of conducting
the surveys each year would increase because
of the new quadrats; (2) age-specific apparent
survival rates and recruitment to the territorial
population could not be estimated with the CJS
analysis because birds would not be marked on
the same area each year; (3) quasi-experiments to
detect the relationship between habitat manipulations
and owl population dynamics would not
be possible; and (4) higher sampling intensities
would be required because this design is less
efficient for estimating change. Our proposed
design is intermediate between sampling the
same set of quadrats each year and a completely
new sample each year. We obtain the benefits
from both alternatives in that the correlation of
measurements for a specific quadrat across years
is used to lower the overall variance of our
population estimate, making the design more
efficient than complete replacement each year,
yet we are guarding against the potential for

sampled quadrats to be managed differently than
other areas.
Conducting Conducting Surveys Surveys Less Less Often Often Than Than Yearly
Yearly
Instead of surveying quadrats each year,
effort and cost could be saved by conducting the
surveys at longer intervals, such as every 5 years.
An advantage of this approach is that costs will
be lowered, and possibly more precise estimates
of population size could be obtained by pooling
money to conduct a few very good surveys
instead of more frequent surveys with lower
effort per survey. The main disadvantage of this
approach is that age-specific apparent survival
rates and recruitment to the territorial population
could not be estimated with the CJS analysis
because birds would not be marked frequently
enough to obtain these estimates. For example,
given an estimate of 0.89 for adult survival, only
56% of the initial population would still be alive
after 5 years, resulting in small sample sizes of
recaptured birds, and hence poorer precision of
the survival estimates. Further, reproductive and
annual survival rates and their variation across
years are needed to realistically evaluate population
viability. Finally, our ability to detect
relationships between habitat manipulations and
population dynamics would be greatly decreased
because this approach is more sensitive to variability
introduced by the years chosen for sampling.
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Adaptive Adaptive Sampling
Sampling
Mexican Spotted Owl Recovery Plan
Thompson (1992) has developed an adaptive
sampling scheme to improve the efficiency of
sampling clustered populations, such as is
probably the case for Mexican spotted owls.
Thompson’s scheme is theoretically appealing
because more effort is applied to areas where
owls are located. Under this approach, quadrats
adjoining a quadrat that contains some threshold
number of spotted owls would also be sampled.
Unfortunately, we cannot envision how to
handle the logistics of adding some unknown
number of quadrats to the sample when survey
crews must be hired, trained, and outfitted with
equipment and vehicles prior to sampling. We
suspect the logistical overhead of this approach
may make it impractical for monitoring owls on
quadrats. However, as the theory and application
of the adaptive sampling scheme is developed
further, an innovative application of the technique
may be possible with our proposed quadrat
monitoring scheme.
CONCLUSION
CONCLUSION
The technology and expertise are available to
monitor trends in Mexican spotted owl habitat
and population size. Clearly, the objectives and
design of the monitoring program must be
defined explicitly and they must be attainable.
To implement the process, knowledgeable,
dedicated people must be assigned the task.
Adequate training and constant feedback mechanisms
are critical aspects to a successful monitoring
program as tenable conclusions can be based
only on reliable data.

The primary objectives of our proposed
research program are to (1) enhance understanding
of Mexican spotted owl biology and (2)
assess how land management practices affect the
owl population’s viability. These types of information
are necessary to complement recovery
efforts outlined in this plan. The research program
described here is different from the monitoring
program outlined in III.C. Whereas both
programs are necessary, specific research needs
may or may not be related to monitoring. In
developing this chapter, we realized that readers
of this plan have a variety of backgrounds. Thus,
to establish a common framework for the discussion
of a research program for the Mexican
spotted owl, we first outline the role of the
scientific process in research and some important
aspects of study design. We then discuss some
limitations with previous research, and suggest
future research questions and processes that
should be examined.
ROLE ROLE OF OF THE THE SCIENTIFIC
SCIENTIFIC
PROCESS
PROCESS
Research and the reliability of knowledge
gained from research depend on appropriate
application of the scientific method. Reliable
knowledge can be defined as “the set of ideas
that agree or are consistent with the facts of
nature,” whereas “unreliable knowledge is the set
of false ideas mistaken for knowledge”
(Romesburg 1981). Three primary scientific
methods have been used in scientific research
(Romesburg 1981): (1) induction that involves
the use of repeated observations to discover laws
of association; (2) retroduction where a “bestguess”
hypothesis is developed to explain a law of
association or some set of observations; and (3)
hypothetico-deductive (HD) where a priori hypotheses
are developed and tested, and a decision
made about whether to reject the hypotheses. It
is generally accepted in science that application
of the HD method provides the best avenue for
gaining reliable knowledge (Platt 1964, Popper
1965, Romesburg 1981, 1991). Steps used in
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D. D. D. ACTIVITY-SPECIFIC
ACTIVITY-SPECIFIC
RESEARCH
RESEARCH
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the HD method can be reiterated as follows
from Nichols (1991): “(1) suggest a hypothesis
to explain some phenomenon of interest, (2)
deduce a testable prediction from that hypothesis,
(3) devise and carry out a suitable test, and
(4) use observations from the test to decide
whether the prediction is met.” When observations
and predictions match, the hypothesis is
corroborated; when they do not match, the
hypothesis has been falsified and can be discarded.
Rejection of hypotheses is key to the HD
method. Corroboration of hypotheses can result
from poor experimental designs (e.g., low
power). Therefore, knowledge in the HD
method is gained more through falsification of
hypotheses than through corroboration.
Most research related to natural resource
management and conservation has relied primarily
on induction and retroduction (Romesburg
1981, 1991). Induction can provide us with
reliable knowledge about associations such as the
association of Mexican spotted owls with forests
having certain structural characteristics. However,
this method does not provide the mechanism
for understanding the processes that
underlie this association nor does it provide
reliable knowledge about cause and effect.
Whereas we can describe the structure of forests
used by spotted owls, we cannot ascertain which
structural characteristics are “important,” or why,
without application of the HD method. In
short, we can describe patterns through induction
but need the HD method to understand
why those patterns occur and which components
of those patterns are “important.” In terms of
management, understanding why a pattern has
occurred and what caused it are important for
predicting effects when observed patterns are
changed.
Romesburg (1981) argued that retroduction
does not provide reliable knowledge because of
the inability of this method to falsify hypotheses
and the large number of alternative hypotheses
that could equally explain the same conclusions.
However, both induction and retroduction are
useful for describing relationships and develop-

ing hypotheses to be further tested using the HD
method. Unreliability of retroduction can be
exacerbated when untested hypotheses are
integrated into our knowledge base as dogma in
the form of scientific “rules.”
While induction and the HD method
provide a general framework for gaining reliable
knowledge, design of appropriate studies is
crucial to the application of this method in
specific situations. This applies to both describing
and understanding patterns in nature. Any
management plan, including the Mexican
Spotted Owl Recovery Plan, is a complex hypothesis
whose rejection or corroboration is
determined by the success or failure of the plan
over the long term.
IMPORTANT IMPORTANT ASPECTS ASPECTS OF
OF
EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL DESIGN
DESIGN
The ability to confidently infer results from a
sample to a population of interest and the
strength of that inference are entirely dependent
on study design. Reliability of knowledge and
the ability to make correct inferences are directly
proportional; the stronger the inference one can
make, the more reliable the knowledge stemming
from that inference. The strongest inference
in understanding patterns is achieved
through controlled experiments, with the
strength of inference diminishing the further a
given study design departs from the experimental
(HD) approach. However, inferences can be
weakened even in experimental studies if the
design is not valid. With Mexican spotted owls,
we would like to extend inferences to a larger
population than the one from which we
sampled. This larger population may be across
the range of the owl, within a certain recovery
unit, or on a Ranger District within a National
Forest. The ability to extend conclusions from a
study to a larger area or a longer time period
depends directly on how the study was designed
and implemented.
For our purposes, study designs can be
characterized as either descriptive or experimental
(following Eberhardt and Thomas 1991).
Descriptive studies employ survey sampling,
whereas experimental studies use treatment and
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control groups. Necessary components of the
design in both cases include: (1) randomization
where samples are randomly selected in a descriptive
study, or treatments and controls are
randomly assigned in an experiment; and (2)
replication of experimental units through both
space and time. Randomization removes subjective
biases that may be found in descriptive
studies and guards against systematic differences
other than treatment effects in experiments.
Randomization also allows for stronger inference
to a larger population and is the theoretical basis
for employing statistical tests. Replication allows
for estimation of experimental error, a prerequisite
for employing statistical tests. If either
randomization or replication are omitted from
an experimental design, inferences will be greatly
weakened. True replication should not be confused
with “pseudoreplication” where
subsampling of experimental units is confused
with replication of experimental units (Hurlbert
1984). For example, a habitat study that measures
100 vegetation plots within each of four
owl home ranges represents a sample of four, not
400. Frequently, researchers are guilty of
pseudoreplication by reporting a sample size of
400. Inferences from such a study apply only to
the 4 owls studied and not to a larger population.
Thus, adequate replication must occur at
the level of the experimental unit (in this case,
number of home ranges) to apply to a larger
population.
A major difficulty in doing field experiments
is that they are performed in an uncontrolled,
“noisy” environment (Eberhardt and Thomas
1991). Therefore, pre- and post-treatment
measurement periods in both control and
treatment groups are needed to reduce the effects
of external variation and to ensure that a treatment
effect can be adequately measured. Additional
important design features necessary in
field experiments include the choice of experimental
units (e.g., owls, owl sites), local control
(amount of balancing and blocking of experimental
units), and the choice of the design (e.g.,
complete block, incomplete block, factorial).
An important consideration when designing
and implementing studies that involve testing
statistical hypotheses is the power of the statistical
test used (the probability of rejecting the null

hypothesis when it is false). Failure to reject a
null hypothesis is due to either (1) the null
hypothesis was indeed “true” or (2) there was
insufficient power to reject it. Thus, power
should be as high as possible (>90%) to corroborate
that an unfalsified null hypothesis was
actually not false. Power is dependent on a
combination of the severity of the treatment
applied, sample size, and experimental error. If a
treatment is subtle, then a larger sample will be
necessary to achieve the same power as if a severe
treatment was used. This is important because
biological questions often involve chronic
(subtle) effects rather than acute (severe) effects.
For example, the effects of a given land management
practice may have a slight effect on adult
survival rates which may in turn have strong
effects on population viability. If an experiment
testing such an effect has low power, then it may
be tempting to state that the practice does not
significantly affect survival rates when in fact it
does. Repercussions from an experiment lacking
sufficient power would then be misleading and
result in false confidence in the health of the
population.
LIMITATIONS LIMITATIONS IN IN PAST
PAST
RESEARCH RESEARCH ON ON THE THE MEXICAN MEXICAN
MEXICAN
SPOTTED SPOTTED OWL
OWL
Previous research on Mexican spotted owls
has been largely descriptive and has relied on
induction and retroduction; our current knowledge
concerning underlying ecological processes
is, therefore, limited. However, previous research
on Mexican spotted owls has provided a good
foundation to describe the natural history of the
species and to generate hypotheses for experimental
tests with the HD method. Additional
limitations on conclusions from previous research
result from (1) lack of randomization in
selecting experimental units and study areas, (2)
lack of true replication (including small sample
sizes), and (3) lack of experiments. The following
discussion is not meant as criticism of
specific research studies or scientists. Many of
the previous studies have been hampered by
inadequate funding and logistical constraints
beyond the investigators’ control. These factors
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Mexican Spotted Owl Recovery Plan
are not unique to research on the Mexican
spotted owl; they are common to research on
numerous species, including both the northern
and California spotted owls.
Lack of randomization and replication has
hampered the ability to infer from particular
samples to the general. In a number of studies,
pseudoreplication has also been confused with
true replication, weakening inferences even
further. For example, most of the habitat studies
using radiotelemetry have suffered from
pseudoreplication. These studies typically
sampled few (4-10) birds, but sampled habitat
characteristics within these few birds’ home
ranges extensively. In testing hypotheses, the
number of subsamples were used, rather than the
number of owls, to estimate error terms used in
statistical tests. Such pseudoreplication lends an
incorrect perception of adequate power to
statistical tests which may lead to incorrect
conclusions. However, repetition of home-range
studies over additional areas has strengthened
inferences concerning certain habitat associations.
Controlled experiments have not been used
in research on Mexican spotted owls. Lack of
experiments is probably related to the need to
quickly identify basic aspects of spotted owl
natural history and apply this information to
management situations. However, experiments
are critical for defining the impacts of current
and proposed management activities on Mexican
spotted owls.
RESEARCH RESEARCH NEEDS
NEEDS
Several management issues and questions
must be resolved to better understand and
implement recovery measures for the Mexican
spotted owl. Communication and collaboration
between people with strong research skills and
people with strong management skills will be a
key component in this process. Managers need
to better understand the methods, problems and
uncertainties involved with research. Researchers,
on the other hand, must rely on managers to
identify appropriate questions, political and legal
constraints, and to develop appropriate implementation
of knowledge derived from research

esults. Too often researchers design and implement
studies that do not adequately address
management problems. People having both
research and management skills will hopefully
bridge the gap between management and research
disciplines. Both time and money are
short. Clearly, all research questions cannot be
answered within a short time frame. Therefore,
we advocate that a series of crucial experiments
be implemented that address questions most
relevant to the needs of management agencies.
The following example of such an experiment
addresses the question, “what structural features
in forest habitat are needed to maintain high
fitness in Mexican spotted owls,” where fitness is
some function of survival and reproduction:
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Determine appropriate statistical hypotheses
(predictions) and response
variables to be tested. Testing fitness
directly through survival and reproductive
rates may not be feasible because of
the prohibitively large samples needed to
detect chronic effects and ethical problems
in purposely affecting survival of
the owls. However, appropriate hypotheses
from the initial question is that
decline in foraging use and prey availability
in altered habitats would directly
affect fitness.
Determine the extent and magnitude of
treatments to apply to forested habitat.
For example, testable research hypotheses
could be that the extent of large trees in
sites affects foraging use by owls and prey
abundance. Treatments may be nested so
that the same experimental units can be
used in repeated experiments, assuming
that treatments can be decided upon
beforehand and applied consecutively. In
addition, treatments need not be “negative”
by removing habitat components
but can be “positive” by treating previously
impacted habitats. Thus, careful
planning is needed at this stage.
Randomly select n spotted owl sites so
that sufficient power can be achieved to
detect differences in foraging by owls
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between treatments. Attach radiotransmitters
to owls within sites.
Collect pre-treatment data and define
high-use areas by owls within all sites.
Randomly assign treatment and control
classifications to the n owl sites.
Apply the treatment to high-use foraging
areas within treatment sites only.
Collect post-treatment data.
Test for differences between treatment
and control groups.
Continue the same procedure with
additional treatments.
While not ideal, such an experiment illustrates
the principles of scientific experimental
design necessary to achieve reliable knowledge
concerning spotted owl habitat use and, indirectly,
fitness, as a function of forest structure.
Such crucial experiments are difficult to design,
require commitments of funding, and scientific
imagination because of ethical constraints and
the limitations on allowable habitat alterations
proposed in this plan. However, these types of
experiments also more rapidly answer pressing
management questions.
We recommend research on the following
questions about Mexican spotted owls that still
need answers. Clearly, a large number of research
questions could be developed that address all
aspects of Mexican spotted owl biology for
which knowledge is lacking. However, we pose
what we believe are the most crucial questions
that need to be addressed in terms of immediate
management problems and the recovery of the
owl. Studies designed to answer these questions
will be descriptive, experimental, or a combination
of both.
Dispersal
Dispersal
Dispersal is a key process in metapopulation
theory and to maintain genetic diversity between

isolated subpopulations (Keitt et al. 1995). Key
questions include:
Genetics
Genetics
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Are subpopulations within and between
Recovery Units connected?
What habitats and large-scale habitat
configurations do dispersing juveniles
require to maintain adequate survival
rates during dispersal?
Mexican spotted owl populations are naturally
fragmented across their range. Genetics can
provide insight into historical connections
between subpopulations. Therefore, questions
on genetics also relate to dispersal. Key questions
include:
Habitat Habitat
Habitat
Are subpopulations within and between
Recovery Units genetically isolated and
to what degree?
What is the extent of genetic interchange
across the entire range of the owl?
Mexican spotted owls use a variety of
habitats ranging from canyons to forested areas
(Ganey and Dick 1995). Key questions include:
To what extent is habitat use determined
by various factors, such as prey availability,
temperature regulation, and/or
avoidance of predators?
What habitat components confer high
fitness?
How do land management activities,
specifically grazing, timber harvest, fire,
and recreation use, proximately affect
habitat use and ultimately affect fitness?
Population Population Biology
Biology
Currently, little is known about Mexican
spotted owl populations. Key questions can be
addressed with our proposed monitoring plan:
Is the Mexican spotted owl population
stable, increasing, or declining?
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Mexican Spotted Owl Recovery Plan
Are some subpopulations increasing
while others are decreasing within the
range of the owl?
Threats Threats to to Recovery
Recovery
Perceived threats need to be examined in
relation to current management strategies to
examine whether these strategies are appropriate
and to develop appropriate management strategies.
Key questions include:
What management strategies can be
employed to reduce to possibility of
catastrophic loss of owl habitat by fire
while maintaining important habitat
components?
To what extent does disturbance from
recreation, vehicles, etc. affect use of sites
by spotted owls?
How does grazing affect prey abundance
in habitats used by spotted owls for
foraging?
Other Other Ecosystem Ecosystem Components
Components
Implementation of the recovery measures for
the Mexican spotted owls will directly and
indirectly affect numerous ecosystem attributes.
Research is needed to determine the extent of
these effects on biotic and abiotic components,
and ecosystem processes and function. Key
questions are:
What are the effects of this recovery plan
on other vertebrates?
What are the effects of implementing the
Plan on nonvertebrates?
What are the effects of implementing the
Recovery Plan on plant community
structure and composition?
What are the effects of implementing the
Recovery Plan on abiotic ecosystem
processes (e.g., hydrological systems)?
What are the effects of implementing the
plan on ecosystem structure and function?
How might the recovery plan be adjusted
to mitigate potentially deleterious effects
on other ecosystem attributes?

The ultimate goal of this Recovery Plan is
to “recover” the Mexican spotted owl from
threatened status. This action is referred to as
“delisting” and is governed by section 4 of the
Act. Delisting the Mexican spotted owl will
require reexamination of the same five factors
considered during every listing process. In
addition, five specific criteria have been developed
to aid the delisting determination. Three of
these criteria pertain to the entire range of the
owl and two refer to a recovery unit level. The
rangewide delisting criteria are:
1. The populations in the Upper Gila
Mountains, Basin and Range-East, and
Basin and Range - West RUs must be
shown to be stable or increasing after 10
years of monitoring, using a study design
with a power of 90% to detect a 20%
decline with a Type I error rate of 0.05.
2. Scientifically-valid habitat monitoring
protocols are designed and implemented
to assess (a) gross changes in habitat
quantity across the range of the Mexican
spotted owl, and (b) whether microhabitat
modifications and trajectories within
treated stands meet the intent of the
Recovery Plan.
3. A long-term, U.S.-rangewide management
plan is in place to ensure appropriate
management of the subspecies and
adequate regulation of human activity
over time.
Once the above three criteria are met,
delisting may occur in any RU that meets the
final two criteria:
4. Threats to the Mexican spotted owl
within the RU are sufficiently moderated
and/or regulated.
5. Habitat of a quality to sustain persistent
Mexican spotted owl populations is
stable or increasing within the RU.
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E. E. SUMMARY SUMMARY OF OF RECOVERY
RECOVERY
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Recovery of the Mexican spotted owl hinges
on successful implementation of three interrelated
programs: population and habitat monitoring,
management guidelines, and research.
These aspects are not intended to stand alone;
thus, all programs must be implemented simultaneously.
For example, monitoring provides a
measure of the effectiveness of the management
guidelines. Without such monitoring, we will
have no basis for determining whether management
guidelines lead to the desired outcomes,
and thus whether the bird should be delisted.
Research is needed to answer key questions
relevant to the Mexican spotted owl, particularly
how implementation of management recommendations
will affect the Mexican spotted owl
and its habitat. The knowledge derived from this
research will provide a scientific basis for revising
short-term guidelines and developing a longterm
management plan.
We have proposed a quadrat sampling
scheme and provide detailed considerations for
determining spotted owl population trends
within the Upper Gila Mountains, Basin and
Range - East, and Basin and Range - West RUs.
Population monitoring is not required for other
recovery units because of sampling constraints
posed by smaller population sizes. The suggested
scheme provides a statistically valid means for
assessing population change Initial cost estimates
for the owl monitoring scheme will range
from $1.2 to $1.5 million per year.
Habitat monitoring is needed to estimate
trends in the quantity and quality of the owl’s
habitat through time. Rangewide monitoring of
the owl’s habitat should be conducted in conjunction
with population monitoring. Because
of the areal extent over which monitoring will be
required, we propose the use of satellite imagery
for tracking gross losses in habitat. We also
propose that field sampling be conducted in
conjunction with planned management treatments.
Treatments include the use of prescribed
fire, thinning, and silviculture. Monitoring
should be done prior to and immediately following
the treatment, and then at five-year intervals.
The objective of this sampling is to determine

changes to microhabitat features and also to
verify that vegetation was placed or continues on
a trajectory to become replacement habitat.
Threats to be moderated include those that
need site-specific treatment to alleviate them,
such as the reduction of the risks of catastrophic
fire. For threats to be considered moderated,
reasonable progress must have been made to
remove identified threats and there must be
adequate assurance that management programs
will continue. Long-term management plans are
needed to guide management after the bird is
delisted. Threats to be regulated include those
resulting from agency management programs or
other anthropogenic activities that are either
ongoing or reasonably certain to occur. These
types of threats include wildfire hazard, timber
harvest, urban or rural land development,
grazing, and recreation.
A primary focus of this Recovery Plan is to
provide recommendations that will moderate or
regulate threats over the short term (10-15
years). Conceptually, this requires the presence
of a mosaic of successional stages throughout a
landscape comprised of the different habitats
used by Mexican spotted owls. The arrangement
and diversity of these habitats must promote the
owl’s persistence. The short-term strategy is
aimed at protecting existing owl habitat and
initiating a process to develop replacement
habitat. Although the approach is not completely
synonymous with ecosystem management,
implementation of the recommendations
should sustain biotic diversity and natural
processes by managing several forest and woodland
systems used by the owl. Recommendations
include management of mixed-conifer and pineoak
forests, and riparian areas. Ponderosa pine
and spruce-fir forests are also considered to a
limited degree.
Several potential threats to the owl were
identified by examining the best available information
on the owl’s biology, and by evaluating
ecological disturbance patterns and current
conditions throughout the owl’s range. Primary
threats include catastrophic fire, timber and
fuelwood harvest, grazing, and recreation. The
magnitude of a threat’s influence on the owl can
vary according to temporal and spatial setting.
For this reason, general recommendations were
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developed by habitat type which apply throughout
the owl’s range, and are emphasized according
to the magnitude of the threats within each
RU. The recommendations were also designed
to provide different levels of protection depending
on the owl’s use of a particular habitat, the
nature of the threats, and management potential.
Our intent was to offer the most specific recommendations
that the best available information
would permit while allowing land managers
flexibility for implementing the recommendations.
Three areas of management are provided
under the general recommendations: protected
areas, restricted areas, and other forest and
woodland types. Protected areas receive the
highest level of protection. Recovery plan
guidelines take precedence over other management
guidelines in protected areas. Guidelines
for restricted areas are less specific and operate in
conjunction with existing management guidelines.
Specific guidelines are not proposed for
other forest and woodland types.
Protected areas are all occupied nest or roost
areas, all areas with slope >40% where timber
harvest has not occurred in the past 20 years,
and all legally administered reserved lands.
Protection of owl nest and roost areas will be
established by designating an area of protection
around an activity center (PAC). This will
require (1) inventory of spotted owls before
planning any management activity that will alter
stand structure; (2) delineating PAC areas of 243
ha (600 ac) for all known Mexican spotted owl
sites, including sites located prior to proposed
management activities; and (3) light burning in
PACs if considered necessary and prudent to
reduce risk of catastrophic loss. Further, a fire
abatement program is proposed to allow treatment
of small fuels within PACs and minimize
probabilities of catastrophic fire. The purpose of
PACs is to provide refugia habitat until it can be
demonstrated reliably that owl habitat can be
created through management. In addition,
harvest of trees 40% where timber harvest
has not occurred in the past 20 years. However,
light burning and prescribed natural fire management
is permitted. Prescribed natural fire is

also encouraged on reserved lands (e.g., wilderness,
Research Natural Areas) where appropriate.
We recommend that management activities
be restricted on some lands outside of protected
areas because patterns of owl use can be expected
to change over time. The guidelines depend
upon forest or woodland type. Silvicultural
prescriptions should emphasize measures to place
stand conditions on a trajectory to become owl
habitat where appropriate. Stands that currently
meet or exceed threshold conditions are subject
to more stringent restrictions than other stands.
Specific management prescriptions should be site
specific and will vary according to short- or
long-term objectives.
Short-term guidelines should not be misconstrued
as onetime management events. For
example, large trees and snags are used by the
spotted owl and will continue to be needed
beyond the life of the plan. Long-term guidelines
are recommended for those activities and
natural processes that combine to influence the
owl and its habitat beyond the life expectancy of
this Recovery Plan.
In addition, riparian communities should be
managed by maintaining broad-leaved forests in
healthy condition where they occur, especially in
canyon-bottoms. Restoration may be necessary
where such forests are not regenerating adequately.
Conceivably, restored riparian forests
could contribute additional nesting, wintering
and dispersal habitat in the future. A mix of
plant size and age classes should be emphasized
in this community, to include large mature trees,
vertical diversity, and other structural characteristics.
No specific guidelines are recommended in
forest or woodland types not typically used by
the owl for nesting. These include ponderosa
pine, spruce-fir, pinyon-juniper, and quaking
aspen in areas outside of PACs. However, some
relevant management of these communities may
produce desirable results for owl recovery.
Examples of guidelines include managing for
landscape diversity, mimicking natural disturbance
patterns, incorporating natural variation
in stand conditions, retaining special features
such as snags, and utilizing fire in an appropriate
manner.
Livestock and wildlife grazing may influence
spotted owls by altering (1) prey availability, (2)
fire risk of some habitats, (3) riparian plant
communities, and (4) development of spotted
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owl habitat. The Team strongly advocates field
monitoring and experimental research related to
impacts of grazing on the Mexican spotted owl.
Other specific guidelines include (1) monitoring
grazing use by livestock and key wildlife species
(e.g. elk, deer), (2) implementing and enforcing
grazing utilization standards that attain good to
excellent range use standards, and (3) protecting
or restoring riparian communities. These guidelines
are emphasized in protected, restricted, and
riparian areas.
Several guidelines for managing recreation in
protected, restricted, and riparian areas are
recommended. These include: (1) no construction,
either of new facilities or for expanding
existing facilities, is allowed within PACs during
the breeding season; (2) construction during the
nonbreeding season should be considered on a
case-specific basis; (3) managers should, on a
case-specific basis, assess the presence and
intensity of allowable recreational activities
within PACs; and (4) seasonal closures of specifically
designated recreation activities should be
considered in extreme circumstances.
Several important questions regarding the
owl’s ecology, and in particular about the effects
of different management activities on the owl’s
population viability, still remain. The Team
recommends additional research on Mexican
spotted owl dispersal, genetics, habitat ecology,
and population biology. Key information that is
vital for refining recovery strategies include (1)
the degree of demographic and genetic isolation
among subpopulations; (2) the relationship
between fitness and specific habitat components;
(3) population trend. Communication and
collaboration between researchers and managers
will be paramount for obtaining necessary
information.
This Recovery Plan presents realistic goals
for recovery of the Mexican spotted owl and its
ultimate delisting. The goals are flexible in that
they allow local land managers to make sitespecific
decisions about management for recovery.
The success of the recovery process hinges
on commitment and coordination among
Federal and State land management agencies,
sovereign Indian Nations, and the private sector
to ensure that the plan is followed and executed
as intended by the Team.

Recovery Plan Implementation
Volume I, Part IV

Part IV discusses laws, regulations, policies,
and authorities directly relevant to implementing
the recovery recommendations included in Part
III. An approach to implementation oversight is
also recommended. Finally, a stepdown outline
of recovery tasks and an implementation schedule
are provided.
This Mexican Spotted Owl Recovery Plan is
based or predicated upon laws that designate
specific legal authority and responsibility to
government agencies for managing public
resources, including wildlife and wildlife habitat.
The following summarizes relevant laws and
authorities applicable to implementation of this
Recovery Plan.
ENDANGERED ENDANGERED SPECIES SPECIES ACT ACT
ACT
Section 2(c)(2) of the Act expresses the
policy of Congress that “...all Federal departments
and agencies shall seek to conserve endangered
species and threatened species and shall
utilize their authorities in furtherance of the
purposes of [the] Act.” Section 7(a)(1) of the
Act requires Federal agencies to “...utilize their
authorities in furtherance of the purposes of the
Act by carrying out programs for the conservation
of endangered species and threatened
species....” Thus, Congress clearly intended
conservation of endangered and threatened
species to be considered in implementation of
Federal programs and actions. In addition, other
Federal laws and regulations require consideration
of endangered and threatened species in
program implementation, including the National
Forest Management Act (NFMA) and the
National Environmental Policy Act (NEPA).
Implementation of the Act is the responsibility
of the Secretary of the Interior for listed
terrestrial species. The Secretary generally delegates
implementation authority to the FWS.
The following sections of the Act are relevant to
implementation of species recovery efforts:
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A. A. A. IMPLEMENTING IMPLEMENTING LAWS, LAWS, LAWS, REGULATIONS,
REGULATIONS,
AND AND AND AUTHORITIES
AUTHORITIES
124
Section Section 4
4
Mexican Spotted Owl Recovery Plan
Section 4 includes the listing and recovery
provisions of the Act, which are discussed in
detail in Part I. Section 4(b) of the Act provides
for designation of critical habitat for endangered
and threatened species. Regulations governing
critical habitat designation are codified at 50
CFR 424. Protection of critical habitat is administered
under section 7 of the Act (discussed
below). Critical habitat is defined under section
3(5)(A) of the Act as:
“(i) the specific areas within the geographical
area occupied by the species...on
which are found those physical or
biological features (I) essential to the
conservation of the species and (II)
which may require special management
considerations or protection; and
(ii) specific areas outside the geographical
area occupied by the species...upon a
determination by the Secretary that such
areas are essential for the conservation of
the species.”
Section 4(d) of the Act provides for promulgation
of special rules for threatened
species only. This allows the Secretary to issue
regulations as deemed necessary for the conservation
of such species. Special rules can be useful
in enacting regulatory provisions uniquely
applicable to the species at hand, and can be
promulgated to avoid unnecessary regulatory
burden. For example, the FWS is considering a
special 4(d) rule to allow small landowners in the
Pacific Northwest to harvest timber and conduct
other activities without risk of violating the
prohibition of incidentally taking (see definition
under Section 9, below) northern spotted owls.

Section Section 5
5
Section 5 directs the Secretary to utilize
funds and authorities of other laws in acquisition
of lands, as deemed appropriate for conservation
of endangered and threatened species.
Section Section 6
6
This section authorizes cooperation with the
States in conservation of threatened and endangered
species. Among its provisions is the authority
to enter into management agreements
and cooperative agreements and to allocate funds
to the States that have entered into such agreements.
Section Section 7
7
Section 7 and its implementing regulations
at 50 CFR 402 govern cooperation between
Federal agencies. Federal agencies must, in
consultation with and with the assistance of the
Secretary, ensure that any action they fund,
authorize, or carry out is not likely to jeopardize
the continued existence of listed species or result
in the destruction or adverse modification of a
listed species’ designated critical habitat. Regulations
at 50 CFR 402 provide the following
definitions:
“‘Jeopardize the continued existence of’
means to engage in an action that reasonably
would be expected, directly or indirectly,
to reduce appreciably the likelihood
of both survival and recovery of a listed
species in the wild by reducing the reproduction,
numbers, or distribution of that
species.”
“‘Destruction or adverse modification’
means a direct or indirect alteration that
appreciably diminishes the value of critical
habitat for both the survival and recovery
of a listed species.”
Section 7 requires action agencies to assess
the effects of proposed actions on listed species
and their critical habitat. If, as a result of that
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125
Mexican Spotted Owl Recovery Plan
assessment, the agency determines that an action
may affect a listed species or its critical habitat,
the agency must enter into consultation with the
FWS. That consultation may result in a biological
opinion from the FWS, in which a determination
is made as to whether jeopardy to the
species and/or destruction or adverse modification
of its critical habitat are likely to result from
the agency action.
If a biological opinion concludes that jeopardy
to the species and/or adverse modification
of its critical habitat are not likely to result from
a proposed action, the action may proceed. The
FWS may provide conservation recommendations
to the agency on ways to minimize or
avoid potential adverse effects on listed species
and/or critical habitat. Implementation of these
conservation recommendations is at the action
agencies’ discretion. In cases where the action is
likely to result in the incidental taking of a
species (see definition under “Section 9,” below),
the Service may provide reasonable and prudent
measures to minimize the amount or extent of
incidental take. The terms and conditions that
accompany and implement any reasonable and
prudent measures are nondiscretionary and must
be implemented. However, reasonable and
prudent measures and their implementing terms
and conditions cannot alter the basic design,
location, scope, duration, or timing of the
action; and they may involve only minor
changes.
If a biological opinion determines that
jeopardy and/or adverse modification is likely to
result from a proposed action, the FWS and the
action agency develop reasonable and prudent
alternatives, if any, to the proposed action.
Reasonable and prudent alternatives refer to
alternative actions that are consistent with the
intended purpose of the proposed action, that
can be implemented within the action agency’s
legal authority, that are economically and technologically
feasible, and that the FWS believes
will not result in jeopardy to listed species or
destruction or adverse modification of critical
habitat. If no reasonable or prudent alternatives
can be identified, the action agency may apply to
the Endangered Species Committee for an
exemption to the prohibition of jeopardy and/or

destruction or adverse modification of critical
habitat.
Section Section 8
8
Section 8 authorizes international cooperation
in conservation of endangered and threatened
species. Included under this section is the
authority to provide financial assistance to
foreign countries to assist in their conservation
efforts.
Section Section 9
9
Section 9 covers prohibited acts in regard to
listed species. Of relevance to the Mexican
spotted owl is the prohibition of taking individuals.
“Take” is defined as “...to harass, harm,
pursue, shoot, wound, kill, trap, capture, or
collect, or to attempt to engage in any such
conduct.” Permits for direct taking of threatened
species may be issued for scientific purposes,
to enhance propagation or survival, in
cases of economic hardship, for zoological
exhibition, or for educational purposes (50 CFR
17.32).
Taking of spotted owls is most likely to
occur through “incidental take.” “Incidental
take” is defined as taking that results from, but is
not the purpose of, carrying out an otherwise
lawful activity. Incidental taking of spotted owls
may result from such activities as timber harvest,
if that activity results in habitat loss to an extent
that an individual spotted owl’s normal behavior
patterns are impaired. In cases where incidental
taking will not result in jeopardy to a listed
species, the FWS may issue an incidental take
statement in a biological opinion on a proposed
Federal action, thereby removing the take
prohibition. Relief from the taking prohibition
for non-Federal activities is discussed under
“section 10” below.
Section Section 10
10
Section 10 authorizes the FWS to issue
permits for takings otherwise prohibited under
section 9. Such permits may be issued for research
purposes and the other situations de-
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Mexican Spotted Owl Recovery Plan
scribed above. In addition, section 10(a)(1)(B)
allows permits for incidental taking that may
result from an activity, provided an applicant
submits a conservation plan that specifies:
“(i) the impact which will likely result
from such taking;
(ii) what steps the applicant will take to
minimize and mitigate such impacts,
and the funding that will be available
to implement such steps;
(iii) what alternative actions to such taking
the applicant considered and the
reasons why such alternatives are not
being utilized; and
(iv) such other measures that the [FWS]
may require as being necessary or
appropriate for purposes of the plan.”
NATIONAL NATIONAL FOREST
FOREST
MANAGEMENT MANAGEMENT ACT
ACT
The NFMA governs Forest Service Management
on National Forest System lands. Section
219.19 (Fish and wildlife resources) states:
“Fish and wildlife habitat shall be managed
to maintain viable populations of existing
native and desired nonnative vertebrate
species in the planning area. For
planning purposes, a viable population
shall be regarded as one which has the
estimated numbers and distribution of
reproductive individuals to ensure its
continued existence is well distributed in
the planning area. In order to ensure that
viable populations will be maintained,
habitat must be provided to support, at
least, a minimum number of reproductive
individuals and that habitat must be
well distributed so that those individuals
can interact with others in the planning
area.”
In formulating alternatives during project
planning, the following is required in regard to
fish and wildlife habitat:
126

“Each alternative shall establish objectives for
the maintenance and improvement of
habitat for management indicator species...to
the degree consistent with overall multipleuse
objectives of the alternative. To meet this
goal, management planning for the fish and
wildlife resources shall meet the requirements
set forth [as follows:]
(1) In order to estimate the effects of each
alternative on fish and wildlife populations,
certain vertebrate and/or invertebrate
species present in the area shall be
identified and selected as management
indicator species and the reasons for their
selection will be stated. These species
shall be selected because their population
changes are believed to indicate the
effects of management activities. In the
selection of management indicator
species, the following categories shall be
represented where appropriate:
Volume I/Part IV
* Endangered and threatened plant and
animal species identified on State and
Federal lists for the planning area;
* Species with special habitat needs that
may be influenced significantly by
planned management programs;
* Species commonly hunted, fished, or
trapped;
* Nongame species of special interest;
and
* Additional plant or animal species
selected because their population
changes are believed to indicate the
effects of management activities on
other species of selected major biological
communities or on water quality.
“On the basis of available scientific
information, the interdisciplinary team
shall estimate the effects of changes in
vegetation type, timber age classes,
community composition, rotation age,
and year-long suitability of habitat
127
Mexican Spotted Owl Recovery Plan
related to mobility of management
indicator species. Where appropriate,
measures to mitigate adverse effects shall
be prescribed.
(2) Planning alternatives shall be stated and
evaluated in terms of both amount and
quality of habitat and of animal population
trends of the management indicator
species.
(3) Biologists from State fish and wildlife
agencies and other Federal agencies shall
be consulted in order to coordinate
planning for fish and wildlife, including
opportunities for the reintroduction of
extirpated species.
(4) Access and dispersal problems of hunting,
fishing, and other visitor uses shall
be considered.
(5) The effects of pest and fire management
on fish and wildlife populations shall be
considered.
(6) Population trends of the management
indicator species will be monitored and
relationships to habitat changes determined.
This monitoring will be done in
cooperation with State fish and wildlife
agencies, to the extent practicable.
(7) Habitat determined to be critical for
threatened and endangered species shall
be identified, and measures shall be
prescribed to prevent the destruction or
adverse modification of such habitat.
Objectives shall be determined for
threatened and endangered species that
shall provide for, where possible, their
removal from listing as threatened and
endangered species through appropriate
conservation measures, including the
designation of special areas to meet the
protection and management needs of
such species.”

NATIONAL NATIONAL ENVIRONMENTAL
ENVIRONMENTAL
POLICY POLICY ACT
ACT
The NEPA requires Federal agencies to
prepare Environmental Impact Statements (EIS)
or Environmental Assessments (EA) for implementation
of agency actions and issuance or
modification of agency policies and guidance.
Impacts of the proposed action or policy amendment
on endangered and threatened species
must be evaluated. If a deciding official determines
that no significant impact will result from
an action or policy amendment, a Finding of No
Significant Impact is issued. If an agency determines
that a significant impact will result from
the proposed action or policy amendment, an
EIS must be prepared. An EIS addresses a range
of alternatives. It is released for public review
and comment, after which an alternative is
selected and a Record of Decision is signed by
the deciding official.
MIGRATORY MIGRATORY MIGRATORY BIRD BIRD TREATY TREATY ACT
ACT
Prior to listing the Mexican spotted owl as
threatened, the Migratory Bird Treaty Act
(MBTA) provided the only Federal protection
for the subspecies other than that afforded by
land-management agencies. Under the provisions
of the MBTA, it is unlawful to pursue,
hunt, take, capture, or kill in any manner any
migratory bird unless permitted by regulations.
The MBTA applies in both the U.S. and
Mexico. Because the Mexican spotted owl
exhibits migratory behavior in some areas it is
included on the list of birds protected under the
MBTA.
Volume I/Part IV
TRIBAL TRIBAL LANDS
LANDS
The Recovery Team encourages adoption of
the recovery recommendations by all Tribes
administering lands that support Mexican
spotted owl habitat. Tribal land-management
regulations and programs, including those for
conservation of species, typically require enactment
by Tribal Councils.
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Mexican Spotted Owl Recovery Plan
STATE STATE AND AND PRIVATE PRIVATE LANDS LANDS
LANDS
Although relatively few Mexican spotted
owls are known on State and private lands, the
Team recommends that States continue and/or
begin a program to inventory forested areas for
the presence of Mexican spotted owls. The
Recovery Team is unaware of any State laws or
regulations that govern management of spotted
owl habitat on State or private lands. The Recovery
Team recommends incorporating the recovery
recommendations into State wildlife and
forest practices laws and regulations. In addition,
the Recovery Team encourages the FWS to
evaluate the importance of State and private
lands to the Mexican spotted owl, and to consider
promulgating a special rule under section
4(d) of the Act that specifies habitat-altering
activities that can be allowed on private lands
without violating the prohibition of incidentally
taking Mexican spotted owls.
MEXICO MEXICO
MEXICO
The Recovery Team is unfamiliar with the
laws, regulations, and authorities that are available
or appropriate for implementing the recovery
recommendations in Mexico. As recommended
later in Part IV, the Recovery Team
expects the FWS to arrange a meeting with
Mexican officials to discuss the Recovery Plan
and its implementation.

Volume I/Part IV
RECOVERY RECOVERY UNIT
UNIT
WORKING WORKING TEAMS TEAMS
TEAMS
The Team strongly recommends formation
of interagency working teams whose responsibility
would be to oversee the implementation of
the Recovery Plan. These Recovery Unit Working
Teams would coordinate with and report to
the Recovery Team, which would evaluate any
Working Team recommendations before passing
them on to the FWS. Working Teams for each
U.S. Recovery Unit should be appointed by the
FWS as subunits under the Recovery Team
umbrella. Recovery Team members may also
serve on Recovery Unit Working Teams if that
arrangement is agreeable. Membership of the
Working Teams should include, at a minimum,
one representative from each of the following:
1. Each involved FWS Ecological Services
Field Office
2. Each involved FS Region
3. Each involved State
4. Each involved Indian Reservation
5. Any other involved agency (e.g., BLM,
NPS).
Each Working Team should have a research
scientist among its membership. That person
may be affiliated with one of the agencies listed
above, or may be independent. In addition to
the above, other interested persons approved by
the Recovery Team and the FWS should be
allowed to participate if they so request. Such
participants may include a representative from a
conservation organization, a representative from
the timber or other affected industry, a representative
from an interested county or other local
government agency, and others as appropriate.
Such a diverse membership would allow ideas of
varying viewpoints to be discussed and would
allow local interested parties to participate in
B. B. B. IMPLEMENTATION
IMPLEMENTATION
OVERSIGHT
OVERSIGHT
129
Mexican Spotted Owl Recovery Plan
plan implementation and resolution of local
issues. Working Teams for each Mexican Recovery
unit should be similarly composed.
Once the FWS formulates a membership
list, that list should be submitted to the Recovery
Team for review. The Recovery Team would
then request the FWS’s Southwest Regional
Director’s approval. Travel costs for each member
would be borne by the member’s agency or
organization.
The functions of the Recovery Unit Working
Teams should include the following:
1. Provide technical assistance to agencies
and landowners on such issues as project
designs, spotted owl management plan
development, and Recovery Plan compliance.
The Recovery Team strongly
encourages conducting Recovery Plan
implementation workshops to provide
biologists, foresters, and other landmanagement
personnel a common
working knowledge of the provisions of
this Recovery Plan. For example, a workshop
to develop procedures for delineating
PACs would encourage consistent
application of recovery recommendations.
Specific workshop recommendations
are provided in IV.C.
2. Provide guidance and interpretation on
implementation of the recommendations
contained in this Recovery Plan.
3. Provide research assistance by procuring
financial and logistic support, screening
research proposals for importance and
relevance, recommending to the Recovery
Team prioritization of research
proposals, and other functions.
4. Recommend Recovery Plan revisions
based on research results that may
enhance recovery efforts in that
specific RU.

5. Prioritize areas to be inventoried within
the RU.
6. Promote communication between
various local interests and help resolve
conflicting interpretations of the Recovery
Plan provisions.
7. Monitor plan implementation and
report problems, successes, and general
recovery progress to the FWS and the
Recovery Team at least annually.
CONTINUING CONTINUING DUTIES DUTIES OF OF THE
THE
RECOVERY RECOVERY TEAM
TEAM
The Recovery Team recommends that it be
continued throughout Recovery Plan implementation.
Once the final Recovery Plan is complete,
the Recovery Team should meet at least
twice per year for the first two years and annually
thereafter. The purpose of these meetings
would be to hear and discuss plan implementation
reports with the Recovery Unit Working
Teams, and to report to the FWS on the progress
of the recovery effort. The Team would also
consider recommendations from Recovery Unit
Working Teams and decide what recommendations
should be brought forward to the FWS as
potential revisions to the Recovery Plan.
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130
Mexican Spotted Owl Recovery Plan
CENTRALIZED CENTRALIZED SPOTTED SPOTTED OWL
OWL
INFORMATION INFORMATION REPOSITORY
REPOSITORY
The Recovery Team recommends that a
central Mexican spotted owl data facility be
maintained throughout the life of the Recovery
Plan. The main purpose of such a facility would
be to house a spotted owl GIS database, including
data assembled through the monitoring
program, inventory program, and other programs
recommended in this Recovery Plan. In
addition, the facility would maintain and periodically
update a Mexican spotted owl bibliography.
Such a facility would be a valuable resource
for biologists, land managers, researchers, and
others who may need information throughout
the plan implementation period. Considerable
information, assembled as a result of development
of this plan, is already stored in a GIS
system maintained by the National Biological
Service’s Midcontinent Ecological Science
Center (formerly the National Ecology Research
Center) in Fort Collins, Colorado; continuance
of that arrangement is recommended by the
Team. In addition, a considerable “Literature
Cited” section is included in this plan, which
should provide a good start to development of a
Mexican spotted owl bibliography.

This section lists specific tasks that need to
be implemented according to the recovery
recommendations in Part III, plus Recovery Plan
oversight provisions discussed earlier in Part IV.
This list is in a stepdown format, as required in
the FWS recovery planning guidelines. Each task
is also listed in Table IV.D.1, where the responsible
parties for task implementation and the
estimated costs of carrying out the tasks are
provided. Tasks are categorized as follows:
1. Resource Management Programs. Many of
the recovery recommendations relate to
spotted owl considerations that shouldbe
incorporated into planning for other
resource management objectives such as
timber harvest, recreation, and management
of other species.
2. Active Management. These recovery
tasks are to be implemented actively.
They include forest health enhancement
and protection, riparian restoration, and
development of a long-term spotted owl
management plan.
3. Monitoring. These recommendations
relate to monitoring the spotted owl
population and habitat.
4. Research. These recommendations
include research studies designed to
increase life-history knowledge of the
subspecies and to test the effects of land
management activities on spotted owls.
5. Oversight, Review, Evaluation, and
Revision. These tasks are necessary to
monitor the Recovery Plan’s effectiveness
and to determine if and when Recovery
Plan revision is necessary.
Volume I/Part IV
C. C. STEPDOWN STEPDOWN STEPDOWN OUTLINE
OUTLINE
131
Mexican Spotted Owl Recovery Plan
1. 1. Resour esour esource esour ce M MManagement
M anagement P PPrograms
PP
ograms
11. Incorporate recovery recommendations
(Part III) into land management
programs.
111. Conduct the NEPA process to
amend appropriate land management
guidance and policy documents
(Federal lands).
1111. FS
1112. BLM
1113. NPS
1114. DOD
112. Incorporate recovery recommendations
into Tribal management plans.
1121. White Mountain Apache
1122. Mescalero Apache
1123. San Carlos Apache
1124. Navajo
1125. Other tribes
113. Incorporate recovery recommendations
into State regulations pertaining
to timber harvests and other
activities on State and private lands.
1131. Arizona
1132. New Mexico
1133. Utah
1134. Colorado
114. Incorporate recovery recommendations
into Mexican policy
documents.
1141. Arrange a meeting between
FWS, Recovery Team, and
Mexican representatives to
discuss provisions of the
Recovery Plan.

Volume I/Part IV
1142. Conduct actions necessary
to officially adopt Recovery
Plan recommendations into
Mexican law and/or policy,
as appropriate.
12. Conduct pre–project Mexican spotted owl
inventories in project areas.
121. Federal agencies
1211. FS
1212. BLM
1213. NPS
1214. DOD
122. Tribes
1221. White Mountain Apache
1222. Mescalero Apache
1223. San Carlos Apache
1224. Navajo
1225. Other tribes
123. States
1231. Arizona
1232. New Mexico
1233. Utah
1234. Colorado
124. Mexico
2. 2. Activ ctiv ctive ctiv e M MManagement
M anagement
21. Develop and/or implement forest
health improvement and protection
programs.
211. Federal lands
2111. FS
2112. BLM
2113. NPS
2114. DOD
2115. Other Federal agencies
212. Tribal lands
2121. White Mountain Apache
2122. Mescalero Apache
132
Mexican Spotted Owl Recovery Plan
2123. San Carlos Apache
2124. Navajo
2125. Other tribes
213. State and private lands
2131. Arizona
2132. New Mexico
2133. Utah
2134. Colorado
214. Mexico
22. Actively manage riparian habitat
(e.g., restore degraded areas).
221. Lowland riparian
2211. BLM
2212. State of Arizona
2213. State of New Mexico
2214. State of Utah
2215. State of Colorado
2216. Mexico
222. Middle to upper elevation riparian
2221. Federal lands
2222. Tribes
22211. FS
22212. BLM
22213. NPS
22214. DOD
22215. Other Federal
agencies
22221. White Mountain
Apache
22222. Mescalero Apache
22223. San Carlos Apache
22224. Navajo
22225. Other tribes
2223. Mexico

23. Develop and implement a long–term,
range wide management plan.
Volume I/Part IV
231. Establish and support a Federal/
Tribal/State/Mexican team to
develop the plan.
232. Develop a draft management plan.
233. Conduct peer/public review.
234. Produce final management plan.
235. Develop appropriate implementation
documents.
3. 3. M MMonitor
M onitor onitoring onitor ing
2351. Joint Federal agency EIS
2352. White Mountain Apache
2353. Mescalero Apache
2354. San Carlos Apache
2355. Navajo
2356. Other tribes
2357. State MOUs
23571. Arizona
23572. New Mexico
23573. Utah
23574. Colorado
2358. Mexico
31. Implement the population monitoring
program detailed in Part III.
311. Secure funding for the entire
monitoring period (up to 15
years).
312. Appoint a principle investigator.
313. Develop detailed study methodology/protocols.
314. Conduct Recovery Team/peer
review of program.
315. Conduct a pilot study.
316. Evaluate and revise methodology/
protocols.
317. Implement the monitoring
program.
32. Implement the habitat monitoring
program detailed in Part III.
321. Macrohabitat
133
4. 4. Research
Research
Mexican Spotted Owl Recovery Plan
3211. Acquire appropriate remote
sensing imagery.
3212. Conduct necessary groundtruthing,
imagery classification,
geo-referencing, etc.
3213. Acquire remote sensing
imagery at year 5.
3214. Conduct necessary groundtruthing,
imager classification,
geo-referencing, etc.
3215. Conduct change-detection
analysis.
3216. Acquire remote sensing
imagery at year 10.
3217. Conduct necessary groundtruthing,
imagery classification,
geo-referencing, etc.
3218. Conduct change-detection
analysis.
322. Microhabitat (ongoing)
3221. Take pre-treatment measurements
of relevant
habitat variables.
3222. Design treatment(s) to
accomplish spotted owl
habitat or other ecosystem
management goals.
3223. Conduct treatment
3224. Take post-treatment measurements
at year 1 of
important habitat variables.
3225. Compare pre- and posttreatment
data to determine
whether objectives of
treatment were met.
3226. Measure habitat variables at
year 5.
3227. Determine whether treated
stands are on appropriate
trajectories.
41. Implement the research recommendations
outlined in Part III.
411. Conduct dispersal studies.

Volume I/Part IV
4111. Examine connectivity of
subpopulations within and
between RUs.
4112. Determine habitat configurations
that best facilitate
dispersal and enhance
survival rates of dispersing
juveniles.
412. Conduct studies on genetics.
4121. Determine whether and to
what degree subpopulations
are genetically isolated.
4122. Determine the extent and
patterns of gene flow across
the landscape.
413. Conduct habitat studies.
4131. Study the extent to which
habitat use is influenced
by prey availability,
microclimatic factors, or
presence of predators.
4132. Determine which habitat
components influence
individual fitness and
population persistence.
414. Study the effects of land-use practices
on spotted owls and/or spotted
owl habitat.
4141. Determine the effects of
various silvicultural and
timber–harvest practices on
spotted owl habitat.
4142. Determine the effects of
livestock and wildlife
grazing on spotted owl
habitat and prey.
4143. Determine the effects of
prescribed fire on spotted
owl habitat and prey.
4144. Determine the effects of
recreational activities on
spotted owl habitat.
134
Mexican Spotted Owl Recovery Plan
415. Study the effects of human
disturbance on spotted owls.
4151. Determine the effects of
noise-producing activities
on nesting spotted owls.
4152. Determine the effects of
suburban and rural development
on habitats and
populations of spotted owls.
416. Study the effects of Recovery Plan
implementation on other ecosystem
components.
4161. Vertebrates and vertebrate
communities
4162. Invertebrates and
invertebrate communities
4163. Plants and plant
communities
4164. Abiotic features
(e.g. hydrological systems)
4165. Ecosystem structure and
functioning
42. Conduct general inventories in areas that
have not previously been inventoried for
spotted owls.
421. Federal lands
4211. FS
4212. BLM
4213. NPS
4214. DOD
4215. Other Federal agencies
422. Tribal lands
4221. White Mountain Apache
4222. Mescalero Apache
4223. San Carlos Apache
4224. Navajo
4225. Other tribes
423. State and private lands
4231. Arizona
4232. New Mexico

Volume I/Part IV
4233. Utah
4234. Colorado
424. Mexico
43. Maintain a centralized Mexican spotted
owl information facility.
431. Establish and maintain a Mexican
spotted owl GIS database.
4311. Establish and annually
update spotted owl location
records and inventory
coverages.
4312. Establish and periodically
update spotted owl habitat
coverages at varying spatial
scales.
432. Develop and periodically update a
spotted owl bibliography.
433. Distribute information to land
mangers and others who request it.
5. 5. Oversight, Oversight, Review, Review, Evaluation,
Evaluation,
and and Revision
Revision
51. Oversee and monitor Recovery Plan
implementation.
511. Conduct section 7 consultation on
any Federal actions that may affect
Mexican spotted owls.
5111. Conduct a workshop
between Recovery Team and
FWS consultation biologists
on evaluation of projects
for Recovery Plan
compliance.
5112. Consult programmatically
on each agency’s incorporation
of the Recovery Plan
into land management
policy and guidance
documents.
5113. Review projects for compliance
with the Recovery
135
Plan.
Mexican Spotted Owl Recovery Plan
512. Form Recovery Unit Working
Teams for each Recovery Unit.
5121. Appoint working Team
members
5122. Develop charter, protocols
for agreeing upon recommendations
to be made to
Recovery Team
(e.g., voting protocols).
5123. Conduct training session
with Recovery Team to
ensure understanding and
consistent interpretation of
the Recovery Plan.
5124. Conduct Recovery Plan
implementation workshops
with biologists and other
land-management
personnel.
5125. Convene approximately
quarterly or as needed.
5126. Working Team Leaders
attend all Recovery Team
meetings.
513. Retain Recovery Team throughout
the life of the Recovery Plan.
5131. Convene Recovery Team
semi–annually for a mini
mum of two years after
Recovery Plan adoption.
5132. Convene Recovery Team
annually thereafter.
52. Oversee Research
521. Recovery Unit Working Teams
should review and prioritize research
proposals and make recommendations
to the Recovery Team.
522. Recovery Unit Working Teams
should annually update the FWS
and the Recovery Team on planned
studies.

53. Review, evaluate, and revise recovery plan
as appropriate.
Volume I/Part IV
531. Recovery Unit Working Teams
should review plan implementation
at least annually, reporting the
results to the FWS and the
Recovery Team.
532. Recovery Unit Working Teams
should review research and suggest
plan revisions, if any, to the FWS
and Recovery Team.
54. Recovery Unit Working Teams should
provide technical assistance when
requested.
541. Provide land managers with technical
assistance in designing projects
to minimize impacts on spotted
owls.
542. Provide technical assistance in
procuring funding and logistic
support for research projects.
136
Mexican Spotted Owl Recovery Plan
543. Provide technical assistance in
developing spotted owl management
plans.
544. Provide technical assistance
in developing conservation
agreements.
545. Provide other technical assistance
as needed.
55. Conduct Mexican spotted owl status
reviews.
56. State and private lands.
561. Conduct assessment of Mexican
spotted owl status on State and
private lands.
562. Promulgate rule under 4(d) of the
Endangered Species Act to provide
for Mexican spotted owl conserva–
tion on State and private lands.

Table IV.D.1 displays estimated costs and
an approximate schedule for implementing the
recovery tasks listed in the stepdown outline
provided in IV.C. More detailed information on
the recommended actions is provided in Part III.
The following material explains relevant details
about Table IV.D.1:
Task ask ask: ask This column lists specific tasks recommended
in Part III. The format of this column is
similar to that used in the stepdown outline in
III.C, with each task under one of five general
task categories (preceded by an Arabic numeral).
In some cases “subtasks” are included if the
Recovery Team wished to identify specific
intermediate actions to accomplish an ultimate
objective. Please refer to the stepdown outline in
III.C for a more detailed description of each
task. Part III provides yet more detail, such as
suggested methodologies and rationales.
Task ask ask N NNo.
N o. o.: o. This column lists the task numbers
as developed in the stepdown outline (IV.C).
P: This column assigns priority numbers as
follows:
1: 1: Tasks that must be completed to achieve
the delisting criteria detailed in III.A.
(Example: Population monitoring); tasks
required by law (Example: Section 7
consultation); and other tasks essential to
Recovery Plan implementation (Example:
amendment of agency planning documents).
2: 2: Tasks that should be done to help attain
the recovery objective. (Example: Restoration
of degraded riparian areas).
3: 3: Tasks that should be done to implement
the Recovery Plan efficiently or to otherwise
enhance spotted owl management.
(Example: general spotted owl inventory).
Dur Dur Dur.: Dur Dur The approximate duration (in years) of
each task. Items that are expected to take less
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D. D. IMPLEMENTATION IMPLEMENTATION AND
AND
COST COST SCHEDULE
SCHEDULE
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Mexican Spotted Owl Recovery Plan
than one year are assigned the number “1.”
Tasks that are ongoing are labeled “cont.” (continuous).
Some tasks can be done to varying
degrees or intensities, particularly research
projects. In those cases, the duration is labeled
“tbd” (to be determined).
Resp. esp. PP
Par PP
ar arty ar ty ty: ty Assigns lead responsibility of each
task to a specific party. This does not necessarily
mean that the indicated entity has sole responsibility
for completion of a specific task; the
Recovery Team recommends that agencies,
Tribes, and others work cooperatively on recovery
tasks whenever possible.
The following abbreviations are used:
AA = As appropriate1 Ac = Action agency
All = All involved2 AZ = State of Arizona
BLM = Bureau of Land Management
CO = State of Colorado
DOD = Department of Defense
FS = Forest Service
FWS= Fish and Wildlife Service
MA = Mescalero Apache
MEX = Mexico
NAV = Navajo
NM = State of New Mexico
NPS = National Park Service
PI = Principle Investigator
RT = Recovery Team
SCA = San Carlos Apache
tbd = to be determined
UT = State of Utah
WMA = White Mtn. Apache
WT = Working Team3 1
Used in situations such as under “Other Federal
agencies.”
2 All parties involved in a cooperative effort, such as the
population monitoring program.
3 Used both for all Recovery Unit Working Teams
collectively, or for the appropriate WT for a Recovery
Unit.

Cost Cost Cost Estimates Estimates: Estimates The figures in this column
represent the estimated costs (x$1,000) of
carrying out the recommended tasks in each
fiscal year (FY) indicated. Estimated costs are
rounded to the nearest $1,000, i.e., a project
estimated at $200 will show “0”; a project
estimated at $500 will show “1”, etc. Some of
the tasks assigned “NA” will be so labeled
because no additional cost attributable to Mexican
spotted owl recovery will be incurred. These
include activities that are either already part of
land management programs or those that can be
paid for through commercial receipts (e.g. forest
health enhancement/protection projects). No
cost estimates are given on tasks for Mexico
because the Recovery Team was unable to obtain
the information.
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Mexican Spotted Owl Recovery Plan
Obviously, it is impossible to accurately
predict the costs of many tasks. For example, the
cost to carry out recommended research activities
can vary widely depending on the study
design, the duration of the study, and other
factors. Similarly, the fiscal year(s) under which
the costs are placed may or may not be the fiscal
year in which the cost is actually incurred; again,
it is impossible predict when a project will be
undertaken. Finally, in cases such as pre-project
inventories, costs can only be estimated on a perunit
basis (e.g., $1.25/acre).

139
Table able IV IV.D.1 IV .D.1 Implementation and Cost Schedule

140
Table able IV IV.D.1 IV .D.1 .D.1, .D.1 continued

141
Table able IV IV.D.1 IV .D.1 .D.1, .D.1 continued

142
Table able IV IV.D.1 IV .D.1 .D.1, .D.1 continued

143
Table able IV IV.D.1 IV .D.1 .D.1, .D.1 continued

144
Table able IV IV.D.1 IV .D.1 .D.1, .D.1 continued

Acronyms Acronyms and and Abbreviations
Abbreviations
Act - Endangered Species Act of 1973, as
amended
AIC - Akaike’s Information Criteria
AK - Adaptive kernel
AOU - American Ornithologists’ Union
ANOVA - Analysis of variance: a statistical
evaluation procedure
AZ - Arizona
BLM - Bureau of Land Management
CJS - Cormack-Jolly-Seber: a population model
CO - Colorado
CSA - Coconino Study Area: a demographic
study area
DOD - Department of Defense
EA - Environmental Assessment
EIS - Environmental Impact Statement
FEMAT - Forest Ecosystem Management
Assessment Team
FS - Forest Service (USDA Forest Service)
FWS - Fish and Wildlife Service (U.S. Fish and
Wildlife Service; USDI Fish and Wildlife
Service)
FY - Federal budget fiscal year; 1 October to 30
September
GIS - Geographic Information System
GSA - Gila Study Area: a demographic study
area
HCA - Habitat Conservation Area
ISC - Interagency Scientific Committee
LMP - Land Management Plan
LRT - Likelihood ratio tests
LSR - Late Successional Reserve
MANOVA - Multivariate analysis of variance
MCP - Minimum convex polygon
MBTA - Migratory Bird Treaty Act
NBS - National Biological Service
NEPA - National Environmental Policy Act
NFMA - National Forest Management Act
NM - New Mexico
NPS - National Park Service (USDI National
Park Service)
PAC - Protected Activity Center
RU - Recovery Unit
SISA - Sky Island Study Area
SOHA - Spotted Owl Habitat Area
SOMA - Spotted Owl Management Area
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GLOSSARY
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Mexican Spotted Owl Recovery Plan
TES - Terrestrial Ecosystem Survey
USDA - United States Department of Agriculture
USDI - United States Department of Interior
USGS - United States Geological Survey
UT - Utah
Ter er erms er ms
Adaptive kernel (AK) - refers to a method of
estimating home-range size. This method
involves estimating a bivariate probability
distribution from the observed animal
locations, and can be used to compute
the area containing a specified proportion
of those locations.
Adaptive management - refers to a process in
which policy decisions are implemented
within a framework of scientifically
driven experiments to test predictions
and assumptions inherent in management
plans.
Algorithm - a mathematical formula for solving
a problem.
Basal area - the cross-sectional area of a tree stem
near its base. Generally measured at
breast height (including bark).
Biomass - with respect to individuals, this refers
to the weight (mass) of a plant or an
animal. With respect to areas or communities,
refers to the total mass of living
organisms in that area or community at
any given time. With respect to owl diet,
used to refer to the relative contribution
of one species (or group) of prey animals
to the overall diet.
Birth-pulse population - a population assumed
to have a discrete point in time during
which all offspring are produced.
Bonferroni confidence interval - a family of
simultaneous confidence intervals in
which the width of each interval is
adjusted downward to account for the
estimation of simultaneous intervals.
Basically, allows for multiple comparisons
without inflating the Type I error
rate.

Bosque - a discrete grove or thicket of trees,
particularly in lowland or riparian areas
of the Southwestern United States and
Mexico; for example a cottonwood
bosque or a mesquite bosque.
Canopy - a layer of foliage, generally the uppermost
layer, in a forest stand. Can be used
to refer to mid- or understory vegetation
in multi-layered stands.
Canopy closure - an estimate of the amount of
overhead tree cover (also canopy cover).
Clearcut - an area where the entire stand of trees
has been removed in one cutting.
Climax species - any species that is characteristic
of a plant community that through
natural processes reaches the apex of its
development after sufficient time. The
opposite of seral species.
Closed population - a population that receives
no immigrants from other populations,
and from which no individuals emigrate
to other populations.
Cohort - individuals of the same age, resulting
from the same birth-pulse.
Commercial forest land - forested land deemed
tentatively suitable for the production of
crops of timber, that has not been
withdrawn administratively from timber
production (see reserved land).
Confidence interval - an interval constructed
around a parameter estimate, in which
that estimate should occur with a specified
probability, such as 95% of the time.
Connectivity - an estimate of the extent to
which intervening habitats connect
subpopulations of spotted owls.
Cordillera - a mountain range or chain.
Cordilleran - of or relating to a range of mountains.
Dbh - diameter at breast height, a standard
measure of tree size.
Demography - the quantitative analysis of
population structure and trend.
Demographic stochasticity - fluctuations in
population size driven by random
fluctuations in birth and death rates.
Dispersal - The movement of organisms from
their birth place to another location
where they produce offspring.
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Mexican Spotted Owl Recovery Plan
Disturbance - significant alteration of habitat
structure or composition. May be natural
(e.g. fire) or human-caused events (e.g.
timber harvest).
Early seral stage - an area that is in the early
stages of ecological succession.
Ecological succession - the orderly progression of
an area through time from one vegetative
community to another in the absence of
disturbance. For example, an area may
proceed from grass-forb through aspen
forest to mixed-conifer forest.
Ecosystem - an interacting biophysical system of
organisms and their environment.
Emigration - permanent movement of individuals
away from a population.
Encinal - of or relating to oaks, particularly plant
communities dominated by live oaks.
Environmental stochasticity - random variation
in environmental attributes, such as
weather patterns or fire regimes.
Even-aged forest - used to refer to forests composed
of trees with a time span of

Fuel ladder - dead or living fuels that connect
fuels on the forest floor to the canopy,
and promote the spread of surface fires
to tree crowns.
Fuel loads - the amount of combustible material
present per unit area.
Fuels - combustible materials.
Fuelwood - wood, either green or dead, harvested
for purposes of cooking or space
heating, and usually measured in cords.
(1 cord = 128 cubic feet.)
Geographical Information System (GIS) - a
computer system capable of storing and
manipulating spatial data.
Gene flow - the movement of genetic material
among populations.
Genetic stochasticity - random changes in gene
frequencies within a population, may
result from factors such as inbreeding
and mutation.
Graminoids - any plants of the grass family in
particular and also those plants in other
families that have a grass-like form or
appearance (for example, sedges).
Group-selection cutting - removal during harvest
of groups of trees.
Habitat - suite of existing environmental conditions
required by an organism for survival
and reproduction. The place where
an organism typically lives.
Habitat fragmentation - see fragmentation.
Habitat mosaic - the mixture of habitat conditions
across a landscape.
Habitat type - see vegetation type.
Hanging canyon - a side canyon, the mouth of
which lies above the floor of a larger
canyon to which it is tributary.
Home range - the area used by an animal in its
day-to-day activities.
Immigration - the movement of individuals
from other areas into a given area.
Intermountain Region - an administrative region
of the USDA Forest Service, lying
between the Pacific Coastal and Rocky
Mountain Ranges and including Utah,
Nevada, southern Idaho, and parts of
Wyoming and Montana.
Lambda - the finite rate of change in population
size. If lambda is greater than 1, the
population trend is increasing; if lambda
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Mexican Spotted Owl Recovery Plan
equals 1, the population trend is stable;
if lambda is less than 1, the population
trend is decreasing.
Land Management Plan (LMP) - a plan written
for the management of a National
Forest. These plans were mandated by
the National Forest Management Act of
1976.
Late seral stage forest - a forest in the latter stages
of development, usually dominated by
large, old trees.
Leslie matrix - a two-dimensional array of
numbers representing age- or stagespecific
estimates of birth and death
rates, used to project population age (or
stage) structure through time.
Life table - mathematical table of age- or stagespecific
birth and death rates of a population.
Macrohabitat - landscape-scale features that are
correlated with the distribution of a
species; often used to describe seral stages
or discrete arrays of specific vegetation
types.
Madrean - pertaining to Mexico’s Sierra Madre
cordillera, or to plant species or communities
whose primary affinity is to that
region (see also Petran).
Madrean pine-oak forest - forests in which any
of several pines characterize the overstory,
and midstory oaks are mostly
evergreen species. Many of the dominant
species are Madrean in affinity. See
Marshall (1957) for descriptions. This
habitat was included as Pine-oak by
Fletcher and Hollis (1994).
Mesic - of or relating to conditions between
hydric and xeric or the specific quality of
being adapted to conditions between wet
and dry.
Metapopulation - systems of local populations
connected by dispersing individuals.
Microhabitat - habitat features at a fine scale;
often identifies a unique set of local
habitat features.
Microtine - any vole of the genus Microtus.
Migration - the seasonal movement from one
area to another and back.
Minimum convex polygon (MCP) - a method
used to estimate home-range size. This

method involves forming a polygon by
connecting the outermost animal locations
with a series of convex lines, then
computing the area of that polygon.
Mixed-conifer forest type - overstory species in
these forests include Rocky Mountain
Douglas-fir, white fir, Rocky Mountain
ponderosa pine, quaking aspen, southwestern
white pine, limber pine, and
blue spruce. Refer to II.C for a more
precise discussion and definition of
mixed-conifer forest type.
Model - a representation of reality, based on a set
of assumptions, that is developed and
used to describe, analyze, and understand
the behavior of a system of interest.
Monitoring - the process of collecting information
to track changes of selected parameters
over time.
Mousing - a technique used to assess reproductive
status of a pair of spotted owls.
Entails feeding mice to adult owls and
observing the owls’ subsequent behavior.
Multi-layered (or multi-storied) stands - forest
stands with >2 distinct canopy layers.
Applied to forest stands that contain
trees of various heights and diameters,
and therefore support foliage at various
heights in the vertical profile of the
stand.
Null hypothesis - a hypothesis stating that there
is no difference between units being
compared.
Other forest and woodland types - vegetation
types that are neither “restricted” or
within PACs (see definitions of those
terms) as to management recommendations
provided in this Recovery Plan.
Old growth - an old forest stand, typically
dominated by large, old trees, with
relatively high canopy closure and a high
incidence of snags, as well as logs and
other woody debris.
Overstory - the highest limbs and foliage of a
tree, and consequently extending and
relating to the upper layers of a forest
canopy.
Pellet - a compact mass of undigested material
remaining after preliminary digestion
and eliminated by regurgitation rather
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Mexican Spotted Owl Recovery Plan
than by defecation.
Peromyscid - any mouse in the genus Peromyscus
of the family Muridae (formerly
Cricetidae).
Petran - pertaining to the Rocky Mountain area.
Used to identify plant associations or
species that have their primary affinity to
the Rocky Mountain area (see also
Madrean).
Physiographic province - a geographic region in
which climate and geology have given
rise to a distinct array of land forms and
habitats.
Pine-oak forest type - stands within the Pinus
ponderosa and Pinus leiophylla series that
exhibit a pine overstory and oak understory.
Refer to II.C for these criteria and
a more precise discussion and definition
of pine-oak forest type.
Precommercial thinning - the practice of removing
some of the smaller trees in a stand
so that remaining trees will grow faster.
Prescribed fire - a fire burning under specified
conditions; may result from either
planned or unplanned ignitions.
Ponderosa pine forest type - any forested stand
of the Pinus ponderosa Series not included
in the pine-oak forest type
definition, or any stand that qualifies as
pure (i.e., any stand where a single
species contributes >80 % of the basal
area of dominant and codominant trees)
ponderosa pine, regardless of the series or
habitat (see also Eyre 1980). Refer to
Part II.C for a more precise discussion
and definition of ponderosa pine forest
type.
Population - a collection of individuals that
share a common gene pool.
Population density - the number of individuals
per unit area.
Population persistence - the capacity of a population
to maintain sufficient numbers
and distribution over time.
Population viability - the probability that a
population will persist for a specific
period of time, despite demographic and
environmental stochasticity.
Power - with respect to statistical comparisons,
refers to the probability of not making a

Type-II error.
Protected Activity Center (PAC) - an area
established around an owl nest (or
sometimes roost) site, for the purpose of
protecting that area. Management of
these areas is largely restricted to managing
for forest health objectives.
Protected areas - as used in this Plan, refers to
areas that are protected, and where most
management activities are very restricted
or disallowed. Includes Protected Activity
Centers.
Recovery - as provided by the Endangered
Species Act and its implementing regulations,
the process of returning a threatened
or endangered species to the point
at which protection under the Endangered
Species Act is no longer necessary.
Recovery Plan - as provided by the Endangered
Species Act, a plan for management of a
threatened or endangered species that
lays out the steps necessary to recover a
species (see “Recovery”).
Recovery Team - a team of experts appointed by
the Fish and Wildlife Service whose
charge is development of a Recovery
Plan (see “Recovery Plan”).
Recovery Unit (RU) - a specific geographic area,
identified mainly from physiographic
provinces, used to evaluate the status of
the Mexican spotted owl.
Recruitment - the addition of individuals to a
population from birth and immigration.
Reserved lands - lands that have been administratively
withdrawn from commercial
activities, such as wilderness areas or
research natural areas.
Restricted Areas - as used in this Plan, refers to
areas that are not protected (see Protected
Areas), but where specific guidelines
for management activities are
proposed.
Riparian - of or relating to a river; specifically
applied to ecology, “riparian” describes
the land immediately adjoining and
directly influenced by streams. For
example, riparian vegetation includes any
and all plant-life growing on the land
adjoining a stream and directly influenced
by that stream.
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Mexican Spotted Owl Recovery Plan
Riparian forests - forests along rivers, streams,
and other wetland environments, typically
characterized by the presence of
riparian-obligate plants such as cottonwoods,
willows, sycamores, or alders.
Descriptions are provided by Dick-
Peddie (1993) and others.
Rocky Mountain Region - An administrative
region of the USDA Forest Service,
including Colorado, Nebraska, South
Dakota, and parts of Wyoming.
Rotation - the planned number of years between
regeneration of a forest stand and final
harvest of that stand.
Salvage - see sanitation salvage.
Sanitation salvage - removal of dead, damaged,
or susceptible trees primarily to prevent
the spread of pests or pathogens and to
promote forest health.
Seed-tree cut - an even-aged regeneration cutting
in which only a few seed trees are retained
per hectare. Shelterwood cuts
retain more seed trees.
Seral species - any plant or animal that is typical
of a seral community (stage).
Seral stage - Any plant community whose plant
composition is changing in a predictable
way; for example, an aspen community
changing to a coniferous forest community.
Shelterwood cut - an even-aged regeneration
cutting in which new tree seedlings are
established under the partial shade of
remnant seed trees.
Silviculture - the practice of controlling the
establishment, composition, and growth
of forests.
Single-tree selection cutting - a cutting method
based on removal of individual trees,
rather than groups of trees (see also
group selection cutting).
Sink - in a population sense, refers to a population
whose death rate exceeds its birth
rate. Such a population is maintained by
immigration from other populations (see
source), and is not expected to contribute
to long-term population maintenance.

Slash - the residue left on the ground after
logging, including logs, uprooted
stumps, branches, twigs, leaves, and bark.
Southwestern Region - an administrative unit of
the USDA Forest Service, including
Arizona and New Mexico; and an administrative
unit of the USDI Fish and
Wildlife Service , including Arizona,
New Mexico, Texas and Oklahoma.
Snag - a standing dead tree.
Source - in a population sense, refers to a population
where birth rate exceeds death
rate. Such a population produces an
excess of juveniles that can disperse to
other populations (see sink).
Spruce-fir forest type - high-elevation forests
occurring on cold sites with short growing
seasons, heavy snow accumulations,
and strong ecological and floristic
affinities to cold forests of higher latitudes.
In general, dominant trees include
Englemann spruce, subalpine and/or
corkbark fir, or sometimes bristlecone
pine. Refer to Part II.C for a more
precise discussion and definition of
spruce-fir forest type.
Stand - any homogeneous area of vegetation
with more or less uniform soils, landform,
and vegetation. Typically used to
refer to forested areas.
Stochastic - random or uncertain.
Stringers - narrow bands of trees that extend into
confined areas of suitable habitat such as
in ravines.
Subpopulation - a well-defined set of individuals
that comprises a subset of a larger,
interbreeding population (see also
metapopulation).
Survivorship - the proportion of newborn
individuals that are alive at any given
age.
Team - the Mexican Spotted Owl Recovery
Team
Technical Team - the Utah Technical Team; an
interagency team charged with providing
management suggestions for the Mexican
spotted owl.
Terrestrial Ecosystem Survey (TES) - a system of
ecosystem classification, inventory,
mapping, and interpretation based upon
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Mexican Spotted Owl Recovery Plan
terrestrial vegetation and environmental
factors, used by the USDA Forest Service,
Southwestern Region. Ecosystems
are defined by combinations of potential
vegetation, soils, and climates. Land is
partitioned into mapping units based
upon inventory data, classification, and
air photo interpretation.
Territory - the area that an animal defends
against intruders of its own species. Not
synonymous with home range, as parts
of the home range are typically shared
with other individuals.
Toe clipping - a procedure by which small
animals are captured alive and marked as
individuals for later recapture recognition
by clipping off portions of one or
more toes in unique combinations.
Trap-night - a standardized measurement of
trapping effort in wildlife studies; equals
one trap set for night. For example, one
trap set for 10 nights and 10 traps set for
one night both equal 10 trap-nights.
Turnover - in a population sense, refers to the
rate at which individuals that die are
replaced by other individuals.
Type-I error - the error made when a null
hypothesis that is true is inappropriately
rejected, as when concluding that two
samples from a single population come
from two different populations.
Type-II error - the error that is made when a null
hypothesis that is false is not rejected, as
when concluding that two samples from
different populations came from a single
population.
Understory - any vegetation whose canopy
(foliage) is below, or closer to the ground
than, canopies of other plants. The
opposite of overstory.
Uneven-aged management - the application of a
combination of actions needed to simultaneously
maintain continuous tall forest
cover, recurring regeneration of desirable
species, and the orderly growth and
development of trees through a range of
diameter or age classes. Cutting methods
that develop and maintain uneven-aged
stands are single-tree selection and group
selection.

Vegetation types - a land classification system
based upon the concept of distinct plant
associations. Vegetation or habitat types
(plant associations) have been documented
for western forests, and keys to
their identification are available. The
primary vegetation (or habitat) types
used by Mexican spotted owls are discussed
in II.C.
Viability - ability of a population to persist
through time (see population viability).
Vital rates - collective term for age- or stage-
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Mexican Spotted Owl Recovery Plan
specific demographic rates, such as birth
and death rates, of a population.
Vole - any small rodent in the genus Microtus,
Clethrionomys, or Phenacomys, all in the
family Muridae.
Witches broom - a mass of profuse and densely
packed twigs representing abnormal
growth of a tree branch. Often results
from infection by dwarf mistletoe.
Xeric - of or relating to perennially dry conditions
or the specific quality of being
adapted to dry conditions.

Alden, P. 1969. Finding the birds in western
Mexico: a guide to the states of Sonora,
Sinaloa, and Nayarit. Univ. Arizona Press,
Tucson. 138pp.
Alexander, B. G., Jr., and F. Ronco, Jr. 1987.
Classification of the forest vegetation on the
National Forests of Arizona and New Mexico.
USDA For. Serv. Res. Note RM-469. Rocky
Mtn. For. and Range Exper. Stn. Fort Collins,
Colo.
——., ——., E. L. Fitzhugh, and J. A. Ludwig.
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65: 324-334.

THE THE RECOVERY RECOVERY TEAM
TEAM
AND AND ASSOCIATES
ASSOCIATES
RECOVERY RECOVERY TEAM:
TEAM:
William M. Block, Team Leader;
Wildlife Biologist.
Education: B.A., Economics, San Diego State
University, 1974; B.S., Wildlife Biology,
Michigan State University, 1981; M.S.,
Wildlife Biology, Humboldt State
University, 1985; Ph.D., Wildland
Resource Science, University of California,
Berkeley, 1989.
Current Position: Project Leader, Research
Wildlife Biologist, USDA Forest Service,
Rocky Mountain Forest and Range
Experiment Station, Flagstaff, Arizona.
Fernando Clemente, Wildlife Biologist.
Education: B.S., Animal Science, University
of Chapingo, Mexico, 1977; M.S.,
Wild Animal Nutrition, Colegio De
Postgraduados, Mexico, 1984; Ph.D.,
Range and Wildlife Management, New
Mexico State University, 1992.
Current Position: Head, Department of Wildlife
Science, and Wildlife Professor, Colegio
De Postgraduados, Campus San Luis
Potosi, Mexico.
James L. Dick, Jr., Silviculturist.
Education: B.S., Forestry, University of Montana,
1967; M.S., Forest Resources,
Pennsylvania State University, 1972.
Current Position: Forester, Recreation Staff Unit,
USDA Forest Service, Southwestern
Region, Albuquerque, New Mexico.
Alan B. Franklin, Spotted Owl Researcher.
Education: B.S., Wildlife Biology, Cornell
University, 1979; M.S., Wildlife Biology,
Humboldt State University, 1987;
Doctoral Candidate, Department of
Fisheries and Wildlife, Colorado State
University.
Current Position: Project Leader, Humboldt
Volume I/Appendix A
APPENDIX APPENDIX A
A
163
Mexican Spotted Owl Recovery Plan
State University Foundation, Humboldt
State University, Arcata, California.
Joseph L. Ganey, Spotted Owl Researcher.
Education: B.S., Wildlife Biology, Humboldt
State University, 1981; M.S., Biology,
Northern Arizona University, 1988;
Ph.D., Zoology, Northern Arizona
University, 1991.
Current Position: Research Wildlife Biologist,
USDA Forest Service, Rocky Mountain
Forest and Range Experiment Station,
Flagstaff, Arizona.
W. H. Moir, Ecologist.
Education: Ph.D., Botany and Soils,
Washington State University, 1965.
Current Position: Research Ecologist, USDA
Forest Service, Rocky Mountain Forest
and Range Experiment Station, Fort
Collins, Colorado.
Sarah E. Rinkevich, Wildlife Biologist.
Education: B.S., Wildlife and Fisheries Science,
University of Arizona, 1987; M.S.,
Wildlife Biology, Humboldt State
University, 1991.
Current Position: Fish and Wildlife Biologist,
USDI Fish and Wildlife Service, New
Mexico Ecological Services State Office,
Albuquerque, New Mexico.
Dean L. Urban, Landscape Ecologist.
Education: B.A., Botany and Zoology, Southern
Illinois University, 1978; M.A., Zoology
(Wildlife Ecology), Southern Illinois
University, 1981; Ph.D., Ecology,
University of Tennessee, 1986.
Current Position: Assistant Professor, School of
Environment, Duke University.
James P. Ward, Jr., Spotted Owl Researcher.
Education: B.S., Wildlife Biology, Humboldt
State University, 1985; M.S., Natural
Resources (wildlife science emphasis),
Humboldt State University, 1990;
Doctoral Candidate, Department of
Biology, Colorado State University.

Current Position: Wildlife Biologist, USDA
Forest Service, Rocky Mountain Forest
and Range Experiment Station, Fort
Collins, Colorado.
Gary C. White, Population Ecologist.
Education: B.S., Fisheries and Wildlife Biology,
Iowa State University, 1970; M.S.,
Wildlife Biology, University of Maine-
Orono, 1972; Ph.D., Zoology, Ohio
State University, 1976; Post Doctorate,
Wildlife Biology, Utah State University,
1976-77.
Current Position: Professor, Department of
Fishery and Wildlife, Colorado State
University, Fort Collins, Colorado.
RECOVERY RECOVERY TEAM-
TEAM-
FISH FISH AND AND WILDLIFE WILDLIFE SERVICE
SERVICE
LIAISON:
LIAISON:
Steven L. Spangle, Fish and Wildlife Biologist —
Regional Listing Coordinator,
USDI Fish and Wildlife Service, Southwestern
Regional Office, Albuquerque,
New Mexico.
CONSULTANTS:
CONSULTANTS:
Pat Christgau, Coordinator, Mexican Spotted
Owl Management, Arizona Game and
Fish Department, Phoenix, Arizona.
Jack F. Cully, Jr., Assistant Unit Leader-Wildlife,
National Biological Service, Kansas
Cooperative Fish and Wildlife Research
Unit, Kansas State University, Manhattan,
Kansas.
Frank P. Howe, Utah Partners in Flight
Volume I/Appendix A
164
Mexican Spotted Owl Recovery Plan
Coordinator, Utah Division of Wildlife
Resources, Salt Lake City, Utah.
Tim Keitt, Graduate Research Assistant,
Department of Biology, University
of New Mexico, Albuquerque, New
Mexico
Tom Spalding, Deputy Director, Arizona
Department of Game and Fish,
Phoenix, Arizona.
Steve Thompson, Biological Technician, Forest
Resources Program, San Carlos Apache
Tribe, San Carlos, Arizona.
Robert Vahle, Program Manager, Arizona
Game and Fish Department,
Region 1, Pinetop, Arizona.
MEETING MEETING FACILITATOR:
FACILITATOR:
FACILITATOR:
Kate W. Grandison, Intermountain Regional
Spotted Owl Coordinator,
Dixie National Forest, Cedar City, Utah.
ADMINISTRATIVE ADMINISTRATIVE ASSISTANT:
ASSISTANT:
Brenda Witsell, Biological Technician, USDA
Forest Service, Rocky Mountain Forest
and Range Experiment Station, Flagstaff,
Arizona.

March 29 to April 4, 1993
Albuquerque, New Mexico
April 27-30, 1993
Flagstaff, Arizona
May 17-21, 1993
Sierra Vista, Arizona
June 23-25, 1993
Alamogordo, New Mexico
July 12-16, 1993
Flagstaff, Arizona
August 16-19, 1993
Pinetop, Arizona
September 14-16, 1993
Fort Collins, Colorado
October 13-15, 1993
Albuquerque, New Mexico
January 10-14, 1994
Flagstaff, Arizona
February 22-25, 1994
Fort Collins, Colorado
March 14-16, 1994
Albuquerque, New Mexico
Volume I/Appendix B
APPENDIX APPENDIX B
B
SCHEDULE SCHEDULE OF OF TEAM TEAM MEETINGS
MEETINGS
165
April 25-29, 1994
Aguascalientes, Mexico
May 23-27, 1994
Cedar City, Utah
June 27 to July 1, 1994
Flagstaff, Arizona
August 8-12, 1994
Flagstaff, Arizona
September 7-9, 1994
Fort Collins, Colorado
September 29, 1994
Albuquerque, New Mexico
October 18-19, 1994
Phoenix, Arizona
February 13-17, 1995
Phoenix, Arizona
June 19-23, 1995
Phoenix, Arizona
July 17-21, 1995
Flagstaff, Arizona
August 14-18, 1995
Albuquerque, New Mexico
Mexican Spotted Owl Recovery Plan

APPENDIX APPENDIX C
C
SCHEDULE SCHEDULE OF OF FIELD FIELD VISITS
VISITS
Mexican Spotted Owl Recovery Plan
DATE DATE
PLACE PLACE PLACE
COORDINATOR
COORDINATOR
April 4, 1993 Walnut Canyon/Bar M Joe Ganey,
Canyon, Coconino NF, Arizona Heather Green
May 20, 1993 Huachuca, Santa Rita and, Russell Duncan
Patagonia Mountains, Arizona Steve Spiech
June 23, 1993 Sacramento Mountains, Danney Salas
Lincoln NF, New Mexico Pat Ward
August 8, 1993 Overflight, Gila NF, Bruce Anderson
New Mexico Steve Servis
August 20, 1993 Fort Apache Indian Reservation, Joe Jojola
Arizona
April 4, 1994 Sierra Fria, National Wildlife Council
Aguascalientes, Mexico
May 11-13, 1994 San Carlos Apache Indian Reservation, Steve Thompson
Arizona Tim Wilhite
May 5, 1994 Zion National Park, Utah Sarah Rinkevich
Volume I/Appendix C
166

A A REFERENCE REFERENCE FOR FOR ENGLISH
ENGLISH
AND AND LATIN LATIN NAMES
NAMES
English names were used in the text of
this Recovery Plan to make smoother reading
and to improve comprehension among people
who are not familiar with Latin names. Names
are arranged in alphabetical order of families for
plants because this is the conventional way of
arranging them in most commonly accessible
tree and wildflower manuals. Species within the
families are listed alphabetically by Latin names.
Animal names are listed phylogenetically, or
taxonomically, because this system prevails in
most commonly accessible books of birds and
mammals, the principal species reported here.
Family names are also provided for the animals
as an aid for further investigation.
Aceraceae
Aceraceae
PLANTS
PLANTS
Canyon Acer
(Bigtooth) maple grandidentatum
Boxelder Acer negundo
Chenopodiaceae
Chenopodiaceae
Shadscale Atriplex sp.
Cupressaceae
Cupressaceae
Arizona cypress Cupressus arizonica
Juniper Juniperus sp.
Ericaceae
Ericaceae
Madrone Arbutus sp.
Manzanita Arctostaphylos sp.
Fabaceae
Fabaceae
Mesquite Prosopis sp.
Volume I/Appendix D
APPENDIX APPENDIX D
D
167
Fagaceae
Fagaceae
Mexican Spotted Owl Recovery Plan
Arizona white oak Quercus arizonica
Quercus chihuahuensis
Quercus coccolobifolia
Emory oak Quercus emoryi
Gambel oak Quercus gambelii
Quercus gentryi
Gray oak Quercus grisea
Silverleaf oak Quercus hypoleucoides
Quercus laeta
Quercus potosina
Quercus resinosa
Netleaf oak Quercus rugosa
Wavyleaf oak Quercus undulata
Papilionoideae
Papilionoideae
Papilionoideae
New Mexico locust Robinia neomexicana
Pinaceae
Pinaceae
White fir Abies concolor
Blue Spruce Picea pungens
Pinyon pine Pinus edulis
Limber pine Pinus flexilis
Western white pine Pinus monticola
Ponderosa pine Pinus ponderosa
Aztec pine Pinus teocote
Southwestern Pinus strobiformis
white pine
Douglas-fir Pseudotsuga menziesii
Redwood Sequoia sempervirens
Platanaceae
Platanaceae
Arizona Sycamore Platanus wrightii
Salicaceae
Salicaceae
Narrowleaf cottonwood Populus angustifolia
Trembling aspen Populus tremuloides
Viscaceae
Viscaceae
Dwarf mistletoe Arceuthobium sp.
Zygophyllaceae
Zygophyllaceae
Creosotebush Larrea sp.

Tortricidae
Tortricidae
ANIMALS
ANIMALS
INVERTEBRATES
INVERTEBRATES
Western Choristoneura
spruce budworm occidentalis
Scolytidae
Scolytidae
Round-headed beetle Dendroctonus
adjunctus
Danaidae
Danaidae
Monarch Butterfly Danaus plexippus
Birds
Birds
Accipitridae
Accipitridae
VERTEBRATES
VERTEBRATES
VERTEBRATES
Golden eagle Aquila chrysaetos
Northern goshawk Accipter gentilis
Red-tailed hawk Buteo jamaicensis
Strigidae Strigidae
Strigidae
Great horned owl Bubo virginianus
Spotted owl Strix occidentalis
California spotted owl S. o. occidentalis
Mexican spotted owl S. o. lucida
Northern spotted owl S. o. caurina
Barred owl Strix varia
Fulvous owl Strix fulvescens
Tawny owl Strix aluco
Psittacidae
Psittacidae
Yellow-headed parrot Amazona ochrocephala
Mammals
Mammals
Soricidae
Soricidae
Masked shrew Sorex cinereus
Vagrant shrew Sorex vagrans
Volume I/Appendix D
168
Mexican Spotted Owl Recovery Plan
Montane shrew Sorex monticouls
Dusky shrew Sorex obscurus
Water shrew Sorex palustris
Leporidae
Leporidae
Desert cottontail Sylvilagus audubonii
Eastern cottontail Sylvilagus floridanus
Nuttall’s cottontail Sylvilagus nuttallii
Sciuridae
Sciuridae
Northern Glaucomys sabrina
flying squirrel
Golden-mantled Spermophilus
ground squirrel lateralis
Rock squirrel Spermophilus
variegatus
Gray-collared Tamias cinereicollus
chipmunk
Gray-footed chipmunk Tamias canipes
Least chipmunk Tamias minimus
Cliff chipmunk Tamias dorsalis
Red squirrel Tamiasciurus
hudsonicus
Geomyidae Geomyidae
Geomyidae
Botta’s pocket gopher Thomomys bottae
Southern pocket Thomomys umbrinus
gopher
Northern pocket Thomomys talpoides
gopher
Heteromyidae
Heteromyidae
Great Basin Perognathus parvus
pocket mouse
Muridae
Muridae
Pinyon mouse Peromyscus truei
Brush mouse Peromyscus boylei
Canyon mouse Peromyscus crinitis
Rock mouse Peromyscus difficilis
Deer mouse Peromyscus
maniculatus
White-footed mouse Peromyscus leucopus
Bushy-tailed woodrat Neotoma cinerea
Desert woodrat Neotoma lepida

Mexican woodrat Neotoma mexicana
Stephens woodrat Neotoma stephensi
White-throated Neotoma albigula
woodrat
Long-tailed vole Microtus longicaudus
Meadow vole Microtus
pennsylvanicus
Mexican vole Microtus mexicanus
Montane vole Microtus montanus
Dipodidae
Dipodidae
Meadow Zapus hudsonius
jumping mouse
Western Zapus princeps
jumping mouse
Volume I/Appendix D
169
Mustelidae
Mustelidae
Mexican Spotted Owl Recovery Plan
Long-tailed weasel Mustela frenata
Trichechidae
Trichechidae
Manatee Trichechus manatus

APPENDIX APPENDIX E
E
AGENCIES AGENCIES AND AND PERSONS PERSONS COMMENTING
COMMENTING
ON ON ON DRAFT DRAFT RECOVERY RECOVERY PLAN
PLAN
Critical review of planning documents by
those that must implement them and others
with relevant expertise is essential to producing
management plans that are scientifically credible
and feasible to implement. This appendix lists
agencies and persons who reviewed the draft
Mexican Spotted Owl Recovery Plan and provided
comments on the document. These
comments are in large part responsible for
production of a final Recovery Plan that the
Recovery Team believes is much improved over
the draft version. Many comments were directly
responsible for Recovery Plan revision, while
many comments that were not incorporated
provoked considerable thought and lively discus-
Mexican Spotted Owl Recovery Plan
sion during the Recovery Plan-revision period.
The Recovery Team is grateful to those who
spent valuable time contributing to this final
Recovery Plan.
PEER PEER PEER REVIEW
REVIEW
The following persons were specifically asked
to review the draft Recovery Plan or portions
thereof, as indicated. “Parts Reviewed” referred
to below relates to the draft Recovery Plan, not
this document. Each persons’ affiliation is listed.
In addition, scientific and professional organizations
that requested an individual’s review are so
indicated.
Commentor Commentor
Par ar arts arts
ts
Review eview eview eviewed eview ed Affiliation Affiliation
Organization rganization
Forsman, E.D. All Pacific Northwest Research American Ornithologists’
Station, U.S. Forest Service Union
Corvallis, OR
Gutiérrez, R.J. I, II Humboldt State University
Arcata, CA
Holthausen, R. I,II, III U.S. Forest Service
Corvallis, OR
King, R. II, III Rocky Mountain Forest and
Range Experiment Station
U.S. Forest Service
Fort Collins, CO
LaHaye, W. II.F, II.G Humboldt State University,
Arcata, CA
Meslow, E.C. All Wildlife Management Institute The Wildlife Society;
Corvallis, OR Wildlife Management
Institute
Morrison, M.L. II.G, II.H University of Arizona
Tucson, AZ
Volume I/Appendix E
170

Commentor Commentor
Par ar arts ar ts
Review eview eview eviewed eview ed Affiliation Affiliation
Organization rganization
Pollock, K.H. II.E, III.A, North Carolina State University
III.D Raleigh, NC
Raphael, M.G. I, II, III Pacific Northwest Research
Station, U.S. Forest Service
Olympia, WA
Stacey, P. II.F, II.G, University of Nevada
III Reno, NV
Verner, J. II.G, III Pacific Southwest Research
Station, U.S. Forest Service
Fresno, CA
AGENCY AGENCY AGENCY REVIEW REVIEW
REVIEW
The following agencies provided comments
on the draft Recovery Plan. Federal agencies are
listed first, followed by State and County agencies.
Agency name is followed by signator; other
reviewers are listed in ( ) when identified by the
agency.
National Park Service, Southern Arizona Group;
Jerry Belson, General Superintendent.
(Benson, L.).
U.S. Bureau of Indian Affairs, Albuquerque Area
Office; Patrick A. Hayes, Area Director.
(Schwab, B.).
U.S. Bureau of Indian Affairs, Southern Ute
Agency; Charles A. Recker, Superintendent.
(Friedley, J.; Recker, T.).
U.S. Bureau of Land Management, Utah; Mat
Millenbach, State Director.
(Stringer, W.).
U.S. Fish and Wildlife Service, Arizona Ecological
Services State Office; Sam F. Spiller,
State Supervisor. (James, M.; Muiznieks,
B.; Palmer, B.).
Volume I/Appendix E
171
Mexican Spotted Owl Recovery Plan
U.S. Fish and Wildlife Service, New Mexico
Ecological Services State Office; Jennifer
Fowler-Propst, State Supervisor.
(Torres, C.).
U.S. Fish and Wildlife Service, Mountain-Prairie
Region; James M. Lutey, Acting Assistant
Regional Director, Ecological Services.
U.S. Forest Service, Southwestern Region;
Charles W. Cartwright, Jr., Regional
Forester. (Beyerhelm, C.; Birkland,
C.; Briggs, A.; Brown, A.; Casper, L.;
Cassidy, R.; Dargan, C.; Deaver, R.;
DeLorenzo, D.; Derby, J.; Ellenwood, J.;
Ewers, S.; Fletcher, R.; Gerritsma, J.;
Green, H.; Herron, M.; Higgins, B.;
Holbrook, C.; Hollis, H.; Holmstrom,
D.; Johnson, D.; Kill, D.; Lucero, L.;
MacIvor, J.; Madril, A.; Manthei, M.;
Martinez, J.; Menasco, K.; Nelson, J.;
Randall-Parker, T.; Rethlake, K.; Rolf, J.;
Schaal, L.; Shafer, J.; Sheppard, G.;
Spoerl, P.; Stahn, R.; Taylor, C,; Vigil,
G.; Wistrand, H.; Zumwalt, M.).
U.S. Forest Service, Intermountain Region; Dale
N. Bosworth, Regional Forester. (Botts,
J.; Egnew, A.; Grandison, K.; Gray, S.;
Hayman, R.).

U.S. Forest Service, Rocky Mountain Region;
Elizabeth Estill, Regional Forester.
(Player, R.).
Arizona Game and Fish Department; Duane L.
Shroufe, Director. (Johnson, T.).
Arizona State Land Department; M. Jean
Hassell, Commissioner.
Otero County Commission; Richard L. Zierlein,
Chairman.
San Juan County Commission;
Ty Lewis, Chairman.
OTHER OTHER GROUPS
GROUPS
AND AND AND INDIVIDUALS
INDIVIDUALS
INDIVIDUALS
Applied Ecosystem Management, Flagstaff, AZ;
Tod Hull. (On behalf of: Northern
Arizona Loggers Association; Precision
Pine and Timber Company; Reidhead
Brothers Lumber Company; Stone
Forest Industries).
Defenders of Wildlife, Washington, DC; Robert
M. Ferris, Director, Species Conservation
Division; Gregory J. Sater, Wildlife
Counsel, Legal Division.
Forest Conservation Council, Santa Fe, NM;
John Talberth, Executive Director.
Volume I/Appendix E
172
Mexican Spotted Owl Recovery Plan
Southwest Center for Biological Diversity, Silver
City, NM; Kieran Suckling, Executive
Director. (Attachment signed by Dennis
Morgan, Research Associate, Southwest
Center for Biological Diversity; Kieran
Suckling, Executive Director, Southwest
Center for Biological Diversity; Sharon
Galbreath, Chairperson, Grand Canyon
Chapter, Sierra Club; Samuel Hitt,
Director, Forest Guardians; Joanie Berde,
Carson Forest Watch; Tom Ribe, Public
Forestry Foundation; Tom H. Wootten,
Conservation Chair, Mesilla Valley
Audubon Society; Mary Lou Jones, Zuni
Mountain Coalition; Joseph Feller; Dave
Henderson, Southwest Forest Alliance;
Charles Babbitt, President, Maricopa
Audubon Society; John Talberth, Executive
Director, Forest Conservation
Council; Jim Powers, Prescott National
Forest Friends; Gary Simpson, Northern
New Mexico Chapter, Wilderness
Watch; Eleanor G. Wooten, Vice President,
T & E, Inc.; Gwen Wardwell,
Director, Rio Grande Chapter, Sierra
Club; Mike Siedman; Jeff Burgess.).
Stone Forest Industries, Flagstaff, AZ; Steve C.
Bennett, Regional Manager.
Mark Herron, Santa Fe, NM.
Terry Johnson, Los Alamos, NM.
Dennis R. Kingsbury, Munds Park, AZ.

Mexican Spotted Owl Recovery Plan
Supporting Documents
Volume II

MEXICAN MEXICAN SPOTTED SPOTTED OWL OWL RECOVERY RECOVERY PLAN
PLAN
Volume Volume Volume II II - - Technical Technical Supporting Supporting Information
Information
Mexican Spotted Owl Recovery Plan
This volume consists of chapters on aspects of Mexican spotted owl natural history that were
developed during preparation of the Mexican Spotted Owl Recovery Plan (Recovery Plan). These
treatises provide much of the information upon which the Recovery Plan, especially the recovery
recommendations in Part III of Volume I, are based. Much of the material in Volume II is highly
technical in nature and, although important, was not considered appropriate for inclusion in a working
implementation document like Volume I of the Recovery Plan. The Mexican Spotted Owl Recovery
Team and the Fish and Wildlife Service believe that these technical papers should, however, be available
to anyone who would like a detailed account of subject matter contained herein.
Since the material detailed in Volume II was integral in developing the Recovery Plan, the salient
points from each of the Volume II chapters are summarized in Part II of Volume I. This makes
Volume I a stand-alone document containing the most relevant information needed to implement the
Recovery Plan and understand the reasons behind the management recommendations contained
therein.
Citations of material contained in this volume should read as follows:
[Author(s)] 1995. Pages [ - ] in USDI Fish and Wildlife Service. Mexican Spotted Owl Recovery
Plan, Volume II.
CONTENTS
CONTENTS
Chapter Chapter 1: 1: D DDistr
D istr istribution istr ibution and and A AAbundance
A bundance
James P. Ward, Jr., Alan B. Franklin, Sarah E. Rinkevich, and Fernando Clemente............... 14 pages
Chapter Chapter 2: 2: P PPopulation
P opulation B BBiolog
BB
iolog iology iolog
Gary C. White, Alan B. Franklin, and James P. Ward, Jr...................................................... 25 pages
Chapter Chapter 3: 3: Landscape Landscape Analysis Analysis and and M MMetapopulation
M etapopulation S SStr
S tr tructur tr uctur ucture uctur
Tim Keitt, Alan B. Franklin, and Dean Urban ................................................................... 16 pages
Chapter Chapter Chapter 4: 4: H HHabitat
H abitat R RRelationships
R elationships
Joseph L. Ganey and James L. Dick, Jr. ............................................................................... 42 pages
Chapter Chapter 5: 5: P PPrey
P ey E EEcolog
E Ecolog
colog cology colog
James P. Ward, Jr. and William M. Block ............................................................................ 48 pages
Volume II i

Chapter Chapter 1
1
Volume II/List of Tables
List List of of Tables
Tables
Mexican Spotted Owl Recovery Plan
Table able 1.1. 1.1. Historical records and minimum numbers of Mexican spotted
owls found during planned surveys .................................................................................................2-3
Chapter Chapter 2
2
Table able 2.1. 2.1. 2.1. Time periods and number of capture histories from three
study areas used in estimating Mexican spotted owl survival. ............................................................. 5
Table able 2.2. 2.2. Apparent survival and recapture probability from three
study areas used in estimating Mexican spotted owl survival .............................................................. 6
Table able 2.3. 2.3. Description of radio-telemetry studies conducted on adult
and subadult Mexican spotted owls ................................................................................................... 8
Table able 2.4. 2.4. Estimates of true survival for Mexican spotted owls
based on radio-telemetry data. .............................................................................................. 9
Table able 2.5. 2.5. Number of management territories checked one or more
times during the Mexican spotted owl monitoring program of FS Region 3 ....................................10
Table able 2.6. 2.6. Persistence of a Mexican spotted owl pair on a territory
for formal and informal monitoring data ........................................................................................10
Table able 2.7. 2.7. Persistence of a pair of Mexican spotted owls on a territory
for the five recovery units contained in the FS Region 3 monitoring data base ................................11
Table able 2.8. 2.8. Estimates of number of young fledged/pair and fecundity
on two demographic study areas .....................................................................................................13
Table able 2.9. 2.9. Mean number of young fledged from 1989-1993,
based on FS monitoring data per pair .............................................................................................14
Table able able 2.10. 2.10. Mean number of young produced/pair from 1989-1993,
based on monitoring data ...............................................................................................................15
Table able 2.11. 2.11. Mean number of young produced per territory from 1989-1993,
based on monitoring data ...............................................................................................................15
Table able 2.12. 2.12. Parameters used to estimate l for Mexican spotted
owls on the GSA and CSA study areas .............................................................................................20
Table able 2.13. 2.13. 2.13. Estimates and standard errors of l for female Mexican
spotted owls on the CSA and GSA study areas ................................................................................20
ii

Mexican Spotted Owl Recovery Plan
Table able 2.14. 2.14. Estimates of population parameters for Mexican
spotted owls on the GSA and CSA study areas ................................................................................21
Table able 2.15. 2.15. Number of Mexican spotted owl territories checked
and the percent of them occupied by a pair of owls for 1989-1993..................................................22
Chapter Chapter 4
4
Table able 4.1. 4.1. Percent of nest and roost sites in various vegetation
types in different Recovery Units ...................................................................................................... 4
Table able 4.2. 4.2. Home-range sizes of radio-marked Mexican spotted owls............................................ 6-7
Table able 4.3. 4.3. Size of nocturnal activity centers of radio-tagged pairs of
Mexican spotted owls in the Upper Gila Mountains and Basin and
Range-East Recovery Units ............................................................................................................... 8
Table able able 4.4. 4.4. Use of forest types for foraging by radio-tagged Mexican spotted
owls on three study areas in northern Arizona. ................................................................................10
Table able able 4.5. 4.5. 4.5. Selected characteristics of nest stands of Mexican spotted owls in
the Upper Gila Mountains and Basin and Range-East Recovery Units.............................................12
Table able 4.6. 4.6. Habitat characteristics sampled at Mexican spotted owl nest sites
on three Ranger districts, Apache-Sitgreaves National Forest, Upper Gila
Mountains Recovery Unit...............................................................................................................14
Table able 4.7. 4.7. Habitat characteristics at Mexican spotted owl nest and
randomly located sites in the Tularosa Mountains, New Mexico; Upper
Gila Mountains RU. .......................................................................................................................15
Table able 4.8a. 4.8a. Habitat characteristics of Mexican spotted owl nest sites
in the Upper Gila Mountains Recovery Unit...................................................................................20
Table able 4.8b. 4.8b. 4.8b. Habitat characteristics of Mexican spotted owl nest sites
in the Basin and Range-East Recovery Unit ....................................................................................21
Table able 4.9. 4.9. 4.9. Habitat characteristics on circular plots within home ranges
of radio-tagged Mexican spotted owls .............................................................................................23
Table able 4.10. 4.10. Habitat characteristics at Mexican spotted owl roost and
random sites in the Tularosa Mountains, New Mexico; Upper Gila
Mountains RU ...............................................................................................................................24
Table able 4.11a. 4.11a. Selected characteristics of roost sites used by radio-tagged
Mexican spotted owls in the Colorado Plateau Recovery Unit. ........................................................27
Table able 4.11b. 4.11b. 4.11b. Selected characteristics of roost sites used by radio-tagged
Mexican spotted owls in the Upper Gila Mountains Recovery Unit ................................................. 28
Volume II/List of Tables iii

iv
Mexican Spotted Owl Recovery Plan
Table able 4.11c. 4.11c. Selected characteristics of roost sites used by radio-tagged
Mexican spotted owls in the Basin and East-Range Recovery Unit ..................................................29
Table able 4.12. 4.12. Seasonal roost site characteristics of radio-tagged Mexican
spotted owls in ponderosa pine-Gambel oak forest, Arizona (Upper
Gila Mountains Recovery Unit) ...................................................................................................... 31
Table able 4.13. 4.13. Characteristics of roost sites used by two migrant Mexican
spotted owls on their winter range ..................................................................................................32
Chapter Chapter 5
5
Table able 5.1. 5.1. Relative frequency of prey items found in the diet of Mexican
spotted owls occurring in the northern portion of the subspecies' range ............................................ 3
Table able 5.2. 5.2. Relative frequency of prey items found in the diet of Mexican
spotted owls occurring in the central portion of the subspecies' range ............................................... 4
Table able 5.3. 5.3. Relative frequency of prey items found in the diet of Mexican
spotted owls occurring in the southern portion of the subspecies' range ............................................ 5
Table able 5.4. 5.4. 5.4. Percent of prey biomass in the diet of Mexican spotted owls
occurring in the northern portion of the subspecies' range ................................................................ 6
Table able able 5.5. 5.5. Percent of prey biomass in the diet of Mexican spotted owls
occurring in the central portion of the subspecies' range ................................................................... 7
Table able able 5.6. 5.6. Percent of prey biomass in the diet of Mexican spotted owls
occurring in the southern portion of the subspecies' range ................................................................ 8
Table able 5.7. 5.7. Animal species consumed by Mexican spotted owls in
18 geographic areas ........................................................................................................................10
Table able 5.8. 5.8. Factors influencing trends observed in Mexican spotted
owl diets................................................................................................................................... 14-15
Table able 5.9. 5.9. Factors influencing production of Mexican spotted owls
in northern Arizona, the Sacramento Mountains, New Mexico, and the
Tularosa Mountains, New Mexico, during 1991, 1992, and 1993 ............................................. 17-18
Table able 5.10. 5.10. Prey comprising ³10% of relative frequency or biomass
in the diet of Mexican spotted owls.................................................................................................21
Table able 5.11. 5.11. Descriptive statistics of selected habitat variables
characterizing habitats of common mammalian prey of Mexican spotted owls ........................... 32-33
Table able 5.12. 5.12. Habitat characteristics used by deer mice in three
vegetation communities of the Sacramento Mountains, New Mexico ............................................ 34
Volume II/List of Tables

Mexican Spotted Owl Recovery Plan
Table able 5.13. 5.13. 5.13. Habitat characteristics used by Mexican woodrats in two
vegetation communities of the Sacramento Mountains, New Mexico ..............................................35
Table able 5.14. 5.14. Habitat characteristics used by long-tailed voles in two
vegetation communities of the Sacramento Mountains, New Mexico ..............................................36
Table able 5.15. 5.15. Habitat characteristics used by Mexican voles in three
vegetation communities of the Sacramento Mountains, New Mexico ..............................................37
Table able 5.16. 5.16. 5.16. Habitat characteristics used by brush mice in xeric forests
of the Sacramento Mountains, New Mexico....................................................................................39
Volume II/List of Tables v

Chapter Chapter 1
1
List List List of of Figures
Figures
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e 1.1. 1.1. Recovery unit boundaries and current distribution of Mexican
spotted owls in the United States ..................................................................................................... 8
Figur igur igure igur e 1.2. 1.2. Current distribution of Mexican spotted owls in Mexico ............................................... 9
Figur igur igure igur e 1.3. 1.3. Density of (a) (a) all three subspecies compared among regions
and (b) (b) (b) Mexican spotted owls among three forest types in the Sacramento
Mountains, New Mexico ................................................................................................................11
Chapter Chapter 2
2
Figur igur igure igur e 2.1. 2.1. Location of Coconino, Gila, and Sky Islands Mexican spotted
owl population study areas in Arizona and New Mexico ................................................................... 5
Figur igur igur igure igur e 2.2. 2.2. 2.2. Changes in occupancy of formal and informal monitoring territories
in the FS Region 3 monitoring database .........................................................................................23
Chapter Chapter 3
3
Figur igur igure igur e 3.1. 3.1. Dispersal-distance relationship for radio-marked juvenile spotted owls ......................... 4
Figur igur igure igur e 3.2. 3.2. The relationship between correlation length and minimum
joining distance. .............................................................................................................................. 8
Figur igur igure igur e 3.3. 3.3. Landscape mosaics of discrete clusters of Douglas-fir and ponderosa
pine habitat types. ........................................................................................................................... 9
Figur igur igure igur e 3.4. 3.4. Change in correlation length due to cluster removal as a function
of distance ......................................................................................................................................10
Figur igur igur igure igure
e 3.5. 3.5. Maps with clusters colored to illustrate their rank importance,
weighted by (uncorrected for) patch area. .......................................................................................11
Figur igur igure igur e 3.6. 3.6. Patch importance to overall connectedness, normalized for patch area. ........................12
Chapter Chapter 4
4
Figur igur igure igur e 4.1. 4.1. Diameter distributions of live trees sampled in nest stands in
the Upper Gila Mountains and Basin and Range - East Recovery Units ...........................................11
Figur igur igure igur e 4.2a. 4.2a. 4.2a. Tree species composition within nest- and random-stand
plots, Upper Gila Mountains Recovery Unit ...................................................................................17
Figur igur igur igure igure
e 4.2b. 4.2b. 4.2b. Tree species composition within nest- and random-stand
plots, Basin and Range-East Recovery Unit .....................................................................................18
Volume II/List of Figures
vi

Volume II/List of Figures vii
Mexican Spotted Owl Recovery Plan
Figur igur igure igur e 4.3. 4.3. Diameter distributions of live trees sampled on nest,
nest stand, and random stand plots ................................................................................................. 19
Chapter Chapter 5
5
Figur igur igure igur e 5.1. 5.1. Cumulative distributions of prey in the diet of
Mexican spotted owls .....................................................................................................................11
Figur igur igure igure
e 5.2. 5.2. Geographic variability in the food habits of
Mexican spotted owls .....................................................................................................................12
Figur igur igure igur e 5.3. 5.3. Reproductive success of Mexican spotted owls in the
Sacramento Mountains, New Mexico, northern Arizona, and Tularosa
Mountains, New Mexico ................................................................................................................19
Figur igur igure igure
e 5.4. 5.4. Biomass of (a) (a) common prey occurring in
mixed-conifer forests, (b) (b) frequencies of peromyscid mice consumed
by Mexican spotted owls, and (c) (c) average number of owl young produced ......................................20
Figur igur igure igure
e 5.5. 5.5. 5.5. Average biomass of common prey of the Mexican spotted owl..................................... 26
Figur igur igure igur e 5.6. 5.6. Trends in average density of common prey
of the Mexican spotted owl ............................................................................................................. 29

Volume II/Chapter 1
CHAPTER CHAPTER 1: 1: Distribution Distribution and and Abundance Abundance
Abundance
of of Mexican Mexican Spotted Spotted Spotted Owls
Owls
James P. Ward, Jr., Alan B. Franklin, Sarah E. Rinkevich,
and Fernando Clemente
Knowledge of the distribution and abundance
of Mexican spotted owls can provide
insight into the subspecies’ geographic limits and
habitat requirements. For example, standardized
surveys for northern spotted owls among different
habitats have provided evidence of the owl’s
affinity for older, densely layered forests
(Forsman et al. 1977; 1987, Thomas et al. 1990,
Blakesley et al. 1992). In addition, distribution
and abundance patterns often provide a foundation
for more intensive natural and life history
studies.
For this recovery plan, we gathered and
examined information on the distribution and
abundance of Mexican spotted owls accumulated
through 1993. We used this information to (1)
document historical and current extent of this
subspecies, (2) help formulate recovery unit
boundaries, and (3) provide a template for
landscape-scale analyses.
SOURCES SOURCES OF OF INFORMATION
INFORMATION
INFORMATION
The quality and quantity of information
regarding the distribution and abundance
Mexican spotted owls varies by source. Historical
accounts exist from museum collections and
anecdotal observations by early natural historians
from throughout the owl’s range (reviewed in
McDonald et al. 1991). These early observations
are useful for documenting the owl’s known
historical range. However, haphazard and frequently
unknown methods by which the historical
information was obtained confound any
attempt to infer change in the owl’s abundance
from historical to present time. Modern accounts
exist from incidental observations provided
by amateur and professional biologists and
from organized surveys conducted by natural
resource management or research personnel.
Incidental observations are similar in quality to
historical accounts, frequently lacking sufficient
information for estimating population parameters
or testing empirical hypotheses. However,
1
Mexican Spotted Owl Recovery Plan
when combined with results of planned surveys
incidental observations can be used to document
the current extent of the subspecies’ range.
Results from planned surveys and demographic
studies have provided the best available data on
the owl’s abundance.
Planned surveys for Mexican spotted owls in
the United States have been conducted by landmanagement
agencies since 1989 and by researchers
in Mexico since 1992. Survey protocols
were reviewed in 1990 and a more formal
program was subsequently developed to locate
Mexican spotted owls (USDA Forest Service
1990). Owl demographic studies began in the
Sky Island Mountains of Arizona in 1990
(Duncan et al. 1993), and in northern Arizona
(Olson et al. 1993) and in the Tularosa Mountains
of west-central New Mexico in 1991
(Seamans et al. 1993).
To document the current (1990-1993)
distribution of the Mexican spotted owl, we
defined an owl site as a visual sighting of at least
one adult spotted owl or as a minimum of two
auditory detections in the same vicinity in the
same year. Observations prior to 1990 are
considered historical records for the purposes of
this report. The methods and limitations of these
data are discussed further in the White et al.
1995.
HISTORICAL HISTORICAL DISTRIBUTION
DISTRIBUTION
We compiled 600 and 35 historical records
of Mexican spotted owls in the United States
and Mexico, respectively (Table 1.1). We refer to
these as records and not as independent sites
because several observations may have been
tallied for the same site. Incomplete information
of the owls’ locations prevented us from assigning
each record to an individual site. Thus, these
records cannot be used to estimate historical
abundance and are presented only to show the
approximate extent of the owl’s distribution
before 1990.

Volume II/Chapter 1
Mexican Spotted Owl Recovery Plan
Table Table 1.1. 1.1. Historical records and minimum numbers of Mexican spotted owls found during planned
surveys, and incidental observations by Recovery Unit and land ownership.
Recovery Recovery Unit
Unit
UNITED UNITED STATES
STATES
Number Number of of owl owl records records
records
before before 1990 1990a
Number Number of of owl owl sites sites
sites
1990 1990 - - - 1993
1993
FS 21 16
BLM 6 10
NPS 34 23
Tribal 20 13b New Mexico State 1 0
Unknownc 5 0
Subtotal Subtotal
87 87
62
62
FS 2 8
BLM 0 6
NPS 0 0
Tribal 1 --b Unknownc 17 0
Subtotal Subtotal
20 20
14
14
FS 25 34
NPS 3 0
New Mexico State 1 0
Private 4 0
Unknownc Colorado Plateau
Southern Rocky Mountains - Colorado
Southern Rocky Mountains - New Mexico
8 0
Subtotal Subtotal
41 41
34
34
Upper Gila Mountains
FS 138 424
BLM 5 0
NPS 5 0
Tribal 20 --b Private 1 0
Unknownc 104 0
Subtotal Subtotal
253 253
424
424
FS 82 97
NPS 13 0
Tribal 0 --b DOD 9 6
Private 8 0
Unknownc Basin and Range - West
57 0
Subtotal Subtotal
169 169
103
103
2

Table Table 1.1. 1.1. 1.1. (continued)
Recovery Recovery Unit
Unit
Volume II/Chapter 1
Number Number of of of owl owl records
records
before before 1990 1990 1990a
Mexican Spotted Owl Recovery Plan
Number Number of of owl owl sites sites
sites
1990 1990 - - 1993
1993
FS 18 111
BLM 1 0
NPS 6 10
Tribal 2 --b UNITED UNITED STATES, STATES, continued continued
continued
Basin and Range - East
FWS 1 0
Private 2 0
Subtotal Subtotal
30 30
121
121
United United States States Total
Total
600 600
758
758
Coahuila 4 0
Nuevo Leon 4 1
Tamaulipas 0 0d MEXICO
MEXICO
Sonora 8 9
Chihuahua 10 8
Subtotal Subtotal Subtotal
8 1
d
Sierra Madre Occidental - Norte
Sinaloa 1 0
Subtotal Subtotal
Sierra Madre Oriental - Norte
19 19
17
17
Coahuila
Sierra Madre Occidental - Sur
2 0
Durango 2 0
Aguascalientes 0 1d Zacatecas 0 0d San Luis Potosi 1 0
Guanajuato 1 0
Subtotal Subtotal
Sierra Madre Oriental - Sur
4 1
Eje Neovolcanico
Jalisco 1 0
Colima 1e 0
Michoacan 1 0
Puebla 1e 0
Subtotal Subtotal
2 0
Mexico Mexico Total
Total
35 35
19
19
a Values do not connote numbers of owls nor owl sites because multiple records may exist from the same site through time.
b Additional owls are known to exist on many Tribal lands but the exact number is unavailable.
c Locations of these records were insufficient for assigning a land ownership.
d Additional sightings have been reported from 1994 surveys.
e Unverified record not included in totals (see text).
3

The general vicinity of all historical records
is presented in the following section according to
RU and land ownership. This information
should help land managers to identify areas that
may be occupied by Mexican spotted owls.
Historical records for owls in the United States
were compiled from several sources which are
cited below. In contrast, much of the historical
information for Mexico was taken from a comprehensive
summary by Williams and Skaggs
(1993).
Colorado Colorado Plateau Plateau Recovery Recovery Unit
Unit
Prior to 1990, Mexican spotted owls were
recorded from Zion (Kertell 1977, Rinkevich
1991), Canyonlands, Capitol Reef (Sue Linner,
FWS, Salt Lake City Utah, pers. comm.), Mesa
Verde (Reynolds and Johnson 1994), and Grand
Canyon National Parks (McDonald et al. 1991),
Glen Canyon National Recreation Area (Behle
1960), and the Cedar City, Richfield, and Vernal
Districts of the BLM (Behle 1981; Sue Linner,
FWS, Salt Lake City, Utah, pers. comm.). Table
1.1 presents more detail regarding these records.
The physical attributes of these historical owl
sites include steep-sided, narrow-walled, or
hanging canyons. The biotic attributes include
coniferous overstory in canyon bottoms with an
understory comprised by Gambel oak, bigtooth
maple, boxelder, and scattered aspen groves near
water (McDonald et al. 1991).
Historical accounts also place the Mexican
spotted owl on the Kaibab Plateau in Arizona
(Ganey and Balda 1989, North Kaibab Ranger
District, unpublished data), plus many sites in
New Mexico. These sites include Fence Lake
(State), Frances Canyon (BLM), the Zuni
Mountains and Mount Taylor (Cibola NF), and
within the Zuni and Navajo Nations (McDonald
et al. 1991, New Mexico Natural Heritage Data
Base, Nature Conservancy, Albuquerque, NM).
Generally, vegetation types reported for these
areas include montane coniferous forests within
canyon settings. The owl has been observed in
steep-walled canyons with minimal vegetation as
well as in forested, steep-sloped canyons on
Black Mesa and in the Chuska Mountains.
Volume II/Chapter 1
4
Mexican Spotted Owl Recovery Plan
Southern Southern Rocky Rocky Mountains Mountains -
-
Colorado Colorado Recovery Recovery Unit
Unit
Eighteen historical records of spotted owls
exist within this unit (Webb 1983, Reynolds
1989). Most of these owls were found along the
Colorado Front Range extending northward to
Fort Collins. Two additional observations, one
each from Rio Grande and San Juan National
Forests, plus one from the Southern Ute Reservation
were recorded during 1989 surveys
(Reynolds and Johnson 1994; Table 1.1).
Historical owl locations in this recovery unit
occurred in steep-sided canyons. These canyons
are typically broader with walls that are not as
vertical as sites occupied by owls in southern
Utah (Colorado Plateau RU). Northern aspects
of these canyons contain mixed-conifer forest,
while southern aspects contain ponderosa pine
and pinyon-juniper. Canyon bottoms contain
Gambel oak and boxelder. Owl sightings in
southwestern Colorado were generally in canyons
that cut into mesas covered with pinyon
and juniper. These canyon bottoms contained
mixed-conifer or ponderosa pine-Gambel oak
forests (McDonald et al. 1991).
Southern Southern Southern Rocky Rocky Mountains Mountains -
-
New New Mexico Mexico Recovery Recovery Recovery Unit Unit
Unit
Mexican spotted owls are known historically
(Table 1.1) from private and National Forest
lands in the San Juan, Sangre de Cristo, and
Jemez Mountains, and near Taos and Sante Fe,
New Mexico (Johnson and Johnson 1985,
McDonald et al. 1991). Incidental observations
between 1979 and 1984 established the presence
of the owl at nine additional sites in the Jemez
Mountains, Sante Fe National Forest (Johnson
and Johnson 1985). The owl has also been
observed in Bandelier National Monument and
near Morhy Lake on State lands (Johnson and
Johnson 1985). Historical spotted owl locations
throughout all of New Mexico (including the
Basin and Range - East RU) have been described
as “deep, narrow, timbered canyons with cool
shady places, at elevations ranging from 6,500
[1,982 sic] to 9,000 ft [2,744 m],” (McDonald
et al. 1991, after Ligon 1926).

Upper Upper Gila Gila Mountains Mountains Recovery Recovery Unit Unit
Unit
Prior to a statewide survey conducted from
1984 through 1988, only one Mexican spotted
owl was recorded from the northern Arizona
(San Francisco Peaks) portion of this RU (Huey
1930). In contrast, several owls were reported for
the National Forest lands in the Mogollon
Highlands of east-central Arizona and westcentral
New Mexico (Ligon 1926, Skaggs 1988).
Forests in those reports include the Apache-
Sitgreaves, Gila, and Cibola National Forests
(Table 1.1). A few observations were also recorded
on BLM land near Bitter Creek, Grant
County and at the Gila Cliff Dwellings National
Monument (NPS), both in New Mexico. Following
their survey of Arizona, Ganey and Balda
(1989) reported 69 sites in the Arizona portion
of the Mogollon Rim and in northern Arizona,
including the Coconino, Kaibab, Tonto, and
Apache-Sitgreaves National Forests. Another 44
records exist in the Arizona Heritage Data Base
(Arizona Game and Fish Department, Phoenix,
AZ). However, the latter records are distributed
among habitats similar to those reported by
Ganey and Balda (1989) and include several of
the same sites.
Site characteristics for the historical Arizona
locations (Ganey and Balda 1989) reflect the
features described for other RU’s: mountain
slopes with mixed-coniferous forest, steep-walled
canyons, or ponderosa pine-Gambel oak forest at
elevations ranging from 1,525 to 2,925 m
(5,000 to 9,590 ft). In southern New Mexico,
Skaggs (1988) found cliffs present at 15 of the
18 historical sites which he examined. However,
it is unclear how many of these sites were located
in the Upper Gila Mountains RU. Skaggs (1988)
also noted a well developed understory of
bigtooth maple and Gambel oak dominated by
mixed-conifer.
Basin Basin and and Range Range - - West West Recovery Recovery Unit
Unit
Historical records for Mexican spotted owls
in this RU include observations in the Huachuca
and Chiricahua Mountains during the 1890s
(reviewed in McDonald et al. 1991). These birds
were observed in a foothills-oak woodland and
Volume II/Chapter 1
5
Mexican Spotted Owl Recovery Plan
in a fir tree in Pinery Canyon, respectively. Two
other sightings were recorded in lowland riparian
communities including an owl nesting in cottonwoods
northwest of Tucson in 1872 and near the
Salt River in 1910 (Bendire 1892, Phillips et al.
1964, McDonald et al. 1991).
More recent surveys found the owl occurring
at 84 sites throughout southern Arizona (Ganey
and Balda 1989). Owls were located in rocky
canyons or in several forest types at elevations
ranging from 1,125 to 2,930 m (3,690 to 9,610
ft) in the Atascosa-Pajarito, Santa Rita, Santa
Catalina, Patagonia, Whetstone, Galiuro,
Huachuca, Chiricahua, Pinaleno, Superstition,
Sierra Ancha, Mazatzal, and Bradshaw Mountains,
Arizona. Below 1,300 m (4,264 ft), spotted
owls were found in steep canyons containing
cliffs and stands of live oak, Mexican pine and
broad-leaved riparian vegetation (Ganey and
Balda 1989). Above 1,800 m (5,904 ft) owls
were found in mixed-conifer and pine-oak
forests. Mid-elevation observations included sites
with Arizona cypress and the other forest types
previously mentioned. The Arizona Heritage
Data Base reports 78 additional records in many
of the same mountain ranges from 1974 to
1989. Historical records on private land include
observations near Animas Peak, Black Bill
Spring, and at the Gray Ranch, in New Mexico
(Skaggs 1988).
Basin Basin and and Range Range - - East East East Recovery Recovery Unit
Unit
Historical locations of Mexican spotted owls
occur on lands of several jurisdictions in New
Mexico: the Organ Mountains and near Bitter
Creek (BLM); the Sandia, Manzano, Sacramento,
and Guadalupe Mountains in the Cibola
and Lincoln National Forests; and Carlsbad
National Park (Skaggs 1988). The owl has also
been found in Guadalupe National Park and on
private land in the Davis Mountains of Texas
(McDonald et al. 1991, Steve Runnels, The
Heard Natural Science Museum and Wildlife
Sanctuary, McKinney, TX, pers. comm.). One
observation each was also reported on the lands
of the Mescalero Apache and at the Santo
Domingo Pueblo (New Mexico Natural Heritage
Data Base, Nature Conservancy, Albuquerque,

NM). Physical and biotic characteristics were
not documented for these various sites. However,
minimal notations describe mixed-conifer forests
on eastern slopes of the Sacramento Mountains
(Skaggs 1988). Canyons were mentioned for
sites near the New Mexico-Texas border of the
Guadalupe Mountains (McDonald et al. 1991).
Sierra Sierra Madre Madre Occidental Occidental -
-
Norte Norte Recovery Recovery Recovery Unit
Unit
More than half of all historical records of
Mexican spotted owls occurring in Mexico have
been reported in this Recovery Unit (Table 1.1).
Owls have been recorded from eight locations in
the State of Sonora prior to 1990. These birds
occurred in the Sierras Pinitos, Azul, de los Ajos,
San Luis, Aconchi, Oposura, and Huachinera
(Williams and Skaggs 1993). The eighth record
was reported from a ridge north of La Mesa,
Mexico. All of these areas are physiographically
and biotically similar to the Sky Island Mountains
of southeastern Arizona (Cirett and Diaz
1993). General elevations at or near these
sightings range from 1,950-2,340 m (6,500 to
7,800 ft). Descriptions of sites at or near the
recorded owls vary. Some descriptions include
dense oaks, pine forest, pine-oak woodland,
cliffs, and a spring with alders and sycamores
(Williams and Skaggs 1993).
Ten historical records have been reported
from the State of Chihuahua (Table 1.1). Owls
have been collected, observed, or heard near
Sierra Carcay, Arroyo Tinaja, Pacheco, Sierra
Azul, Colonia Garcia, Sierra del Nido, Rancho
La Estancia, Yaguirachic, Pinos Altos, and
Vosagota (Williams and Skaggs 1993). Elevations
at or near these sightings range from
1,710-2,700 m (5,700 to 9,000 ft). Most of
these observations were made in or near pineoak
woodlands (Williams and Skaggs 1993).
Owls have also been reported in canyons with
oaks and madrone, and in subalpine forest
comprised of Douglas-fir, true firs, oak, alder,
pines, and chokecherry.
In Sinaloa, one spotted owl was observed
near Rancho Liebre Barranca (Williams and
Skaggs 1993). This area consists of deeply
dissected barrancas with pine and oak forest at
Volume II/Chapter 1
6
Mexican Spotted Owl Recovery Plan
higher altitudes and a mixture of temperate and
tropical forest in canyon bottoms.
Sierra Sierra Madre Madre Oriental Oriental -
-
Norte Norte Recovery Recovery Unit
Unit
Spotted owls have only been reported from
two sites within this Recovery Unit. Both
records are from the Sierra la Madera of central
Coahuila (Table 1.1). One owl was observed
roosting in a “cliff-lined canyon bottom under a
dense canopy of maples and oaks” in Canada el
Agua (Williams and Skaggs 1993). Another owl
was observed and heard in a “garden-like” arroyo
containing pines, oaks, and madrones (Williams
and Skaggs 1993). Elevations of these observations
were approximately 1,900 and 2,100 m
(6,200 and 7,000 ft), respectively.
Sierra Sierra Madre Madre Occidental Occidental Occidental -
-
Sur Sur Recovery Recovery Unit Unit
Unit
Four historical records exist from the States
of Durango, San Luis Potosi, and Guanajuato
(Table 1.1). In Durango, spotted owls have been
observed near Espinazo del Diablo in mixedconifer
forest and on two occasions in the
Michilia Biosphere Reserve. One of the owls
found in the reserve was observed roosting in a
large oak that was in a cool, wet ravine. The
second owl was found in a pine-oak forest.
Remaining records are of two spotted owls
collected at approximately 2,400 m (8,000 ft)
near Cerro Campanario, San Luis Potosi, and
another that was collected in the State of
Guanajuato (Williams and Skaggs 1993).
Sierra Sierra Madre Madre Oriental Oriental Oriental -
-
Sur Sur Recovery Recovery Unit
Unit
In this Recovery Unit, eight records of
spotted owls have been reported from two States,
Coahuila and Nuevo Leon (Table 1.1). Owls
have been heard and observed on several occasions
east of Saltillo, Coahuila. Elevations of
these records are generally higher than other
historical sightings and range from 2,700-3,060
m (9,000 to 10,200 ft). The vegetation at these
sites has been described as oak-pine-conifer

woodland or as oak-pine woodland. Cliffs are
present at all sites and chaparral or desert scrub
vegetation can also be seen at two of these sites
(Williams and Skaggs 1993). In addition, two of
the four historical records from Nuevo Leon are
from the mountains east of Saltillo and south of
Monterrey. At one of these sites a spotted owl
was heard calling from an oak-pine-conifer
forest, approximately 2,550 m (8,500 ft) in
elevation. The second was heard calling from an
“oak-pine woodland mixed with Tamaulipan
thorn woodland and scrub and palms on the
canyon cliffs” (Williams and Skaggs 1993). The
elevation at this site was 1,350 m (4,500 ft), the
lowest to be recorded for spotted owls in
Mexico. The remaining two Nuevo Leon records
are from the slopes of Cerro Potosi (Williams
and Skaggs 1993). One female spotted owl was
collected at 2,250 m (7,500 ft) in 1946. Another
owl was heard in 1978 from a pine woodland
near the summit at 3,630 m (12,100 ft), the
highest elevation recorded for a Mexican spotted
owl.
Eje Eje Neovolcanico Neovolcanico Recovery Recovery Unit Unit
Unit
Only two confirmed records of Mexican
spotted owls exist for the southernmost Recovery
Unit (Table 1.1). Specimens of spotted owls have
been collected from the States of Jalisco and
Michoacan. Two other records from the States of
Colima and Puebla have been published
(Enriquez-Rocha et al. 1993) but have not been
verified (Williams and Skaggs 1993).
In Jalisco, the owls were found on the north
slope of Cerro Nevado de Colima in a park-like
pine forest with broad-leaved oaks, and mesic
ground flora near 2,400 m (8,000 ft) elevation
(Williams and Skaggs 1993). In Michoacan, the
holotype of the subspecies and only existing
State record was collected in 1903 from Cerro
Tancitaro above 1,950 m (6,500 ft). Details
regarding the spotted owls allegedly collected in
Colima and Puebla have not been reported
(Enriquez-Rocha et al. 1993). We mention these
latter records because they suggest possible
extensions of the owl’s range. However, we have
not included them in the totals presented in
Table 1.1.
Volume II/Chapter 1
7
Mexican Spotted Owl Recovery Plan
CURRENT CURRENT DISTRIBUTION
DISTRIBUTION
AND AND ABUNDANCE
ABUNDANCE
Number Number of of Sites
Sites
Surveys for Mexican spotted owls conducted
from 1990 through 1993 indicate that the
species persists in most locations reported prior
to 1989. Notable exceptions include riparian
habitats in the lowlands of Arizona and New
Mexico, and all previously occupied areas in the
southern States of Mexico. As a result of planned
surveys, additional sightings have been reported
for all recovery units. New locations will undoubtedly
be reported following future surveys.
The current known range of the Mexican
spotted owl extends north from Aguascalientes,
Mexico, through the mountains of Arizona, New
Mexico, and western Texas to the canyons of
southern Utah, southwestern Colorado, and the
Front Range of central Colorado (Figures 1.1
and 1.2). Results from planned surveys and
incidental observations conducted during 1990
through 1993 indicate one or more owls have
been observed at a minimum of 758 sites in the
United States and 19 sites in Mexico (Table 1.1).
The greatest concentration of the known
sites in the United States occurs in the Upper
Gila Mountains Recovery Unit (55.9%) followed
by the Basin and Range-East (16.0%),
and Basin and Range-West (13.6%), Colorado
Plateau (8.2%), Southern Rocky Mountains -
New Mexico (4.5%), and Southern Rocky
Mountains - Colorado (1.8%) Recovery Units.
Thus, fewer owl sites are currently known to
occur north of the Upper Gila Mountains
Recovery Unit (12.7%) than to the south of this
recovery unit (29.6%). In Mexico, the majority
of spotted owls have been documented in the
Sierra Madre Occidental - Norte RU (89.5%).
However, the number of identified sites within a
given RU depends on survey intensity for which
we have little reliable data. Therefore, the percentages
of sites within a given RU may not
reflect the true relative abundance of Mexican
spotted owls.

Volume II/Chapter 1
Mexican Spotted Owl Recovery Plan
Figure Figure 1.1. 1.1. Recovery unit boundaries and current distribution of Mexican spotted owls in the
United States based on planned surveys and incidental observations recorded from 1990 through 1993.
FPO
8

Volume II/Chapter 1
FPO
Mexican Spotted Owl Recovery Plan
Figure Figure 1.2. 1.2. Current distribution of Mexican spotted owls in Mexico based on planned surveys and
incidental observations recorded from 1990 through 1993.
9

Number Number of of Owls
Owls
A reliable estimate of the number of Mexican
spotted owls throughout its entire range is not
available. Fletcher (1990) calculated that 2,074
owls existed in Arizona and New Mexico in
1990 using information gathered by the FS,
Southwestern Region. McDonald et al. (1991)
modified Fletcher’s (1990) calculations reporting
a total of 2,160 owls in the United States. If one
assumes that all 758 sites included in this recovery
plan were occupied by owl pairs, then at least
1,516 adult or subadult owls were known to
exist in the United States and 38 adult or subadult
owls in Mexico from 1990 through 1993.
These numbers are not reliable estimates of
current population size because no measures of
bias or precision can be produced. Further, the
amount of survey effort devoted to deriving
these numbers cannot be reliably calculated, nor
is an accurate measure available for areas or
habitats surveyed. Thus, we did not believe it
would be useful to estimate the size of the
Mexican spotted owl population given the
limited quality of data currently available. At
best, our total numbers reported in Table 1.1
represent a range for the minimum number of
owls known to exist during some portion of a
four year period in the United States and Mexico
(777 individuals if each site was occupied by a
single owl to 1,554 individuals if each site was
occupied by a pair).
Density
Density
The abundance of any terrestrial organism is
more appropriately presented as density, the
number of individuals per unit of area (Caughley
1977), hereafter referred to as “crude density”
(Franklin et al. 1990). Because the Mexican
spotted owl occupies a variety of habitats
throughout its range, ecological density, the
number of individuals per area of usable habitat,
(Tanner 1978) would be a more meaningful
measure of abundance. At this time, rangewide
estimates of either crude or ecological density of
Mexican spotted owls cannot be provided for the
same reasons that population numbers cannot be
estimated reliably.
Volume II/Chapter 1
10
Mexican Spotted Owl Recovery Plan
^
Two estimates of crude density (D) exist
from studies conducted at either end of the
Upper Gila Mountains Recovery Unit. These
estimates were reported for the Coconino Study
Area (CSA) in northern Arizona and for the Gila
Study Area (GSA) in west-central New Mexico
by Gutiérrez et al. (1994). Density of adult and
subadult owls in both studies was estimated
using a count of individuals divided by the size
of the study area (CSA: 484 km2 [187 mi2 ];
GSA: 323 km2 [125 mi2 ]). Identity of owls was
established by capturing and marking or by
direct observation at daytime roosts when
marking was not possible. Methods were similar
to those reported for northern spotted owls by
Franklin et al. (1990) and Ward et al. (1991) and
resulted only in density of territorial individuals.
Only the 1993 estimates of density (D) are
presented here because the boundaries of the
CSA study area were shifted between 1991 and
1992.
D of Mexican spotted owls in 1993 was
0.120 owls/km2 (0.310 owls/mi2 ) in the CSA
and 0.180 owls/km2 (0.464 owls/mi2 ) in the
GSA. The CSA has more ponderosa pine-
Gambel oak forest (72.6%) and less mixedconifer
forest (14.4%) than the GSA (22.3%
and 28.5%, respectively; Gutiérrez et al. 1994).
The larger proportion of mixed-conifer may
partially explain higher owl density in the GSA.
For comparison (Figure 1.3a), 1993 density of
California spotted owls in the San Bernardino
Mountains, California (LaHaye and Gutiérrez
1994) was 0.118 owls/km2 (0.305 owls/mi2 ) and
density of northern spotted owls in northwestern
California (Franklin, unpublished data) was
0.272 + 0.004 (SE) owls/km2 (0.703 + 0.009
owls/mi2 ). Survey methods used in these later
two studies were identical to those used in the
CSA and GSA. Naive density estimates, the
number of owls counted divided by study area
size, were used in this comparison (Figure 1.3a)
except for the northern spotted owl population.
In the latter case, a Jolly-Seber model was used
to estimate numbers of owls and an associated
sampling variance. The two density estimators
are similar for spotted owls (Ward et al. 1991).
Combining the CSA and GSA density data
and weighting by area provides an average
estimate of 0.144 owls/km2 (0.372 owls/mi2 ^
^
)

Volume II/Chapter 1
FPO
FPO
Mexican Spotted Owl Recovery Plan
Figure Figure Figure 1.3. 1.3. 1.3. Density of (a) (a) all three subspecies compared among regions and (b) (b) Mexican spotted
owls among three forest types in the Sacramento Mountains, New Mexico, based on Skaggs and Raitt
(1988). Sources of estimates for northern Arizona (CSA) and west-central New Mexico (GSA) are from
Gutiérrez et al. (1994); southern California are from LaHaye and Gutiérrez (1994); and northwestern
California are from Franklin (unpublished data). Vertical bars are 95% confidence intervals.
11

within the Upper Gila Maintains RU. However,
this estimate should not be extrapolated to a
larger area because (1) the CSA and GSA were
not randomly selected and (2) studies were not
sufficiently replicated. Both of these problems
could severely bias extrapolated estimates because
the areas studied are not necessarily representative
samples of the entire recovery unit or
subspecies’ range.
In another study, Skaggs and Raitt (1988)
examined the density of Mexican spotted owls
among three forest types in the Sacramento
Mountains (Basin and Range - East RU). Eighteen
23.1- km 2 (9-mi 2 ) quadrats, six in each
forest type, were surveyed for spotted owls.
Quadrats were classified as pinyon-juniper
woodland, pine, or mixed-conifer forest according
to the most common tree species within the
quadrat. Owl density averaged across the three
forest types (x = 0.126 owls/km 2 [0.325
owls/mi 2 ]) was similar to the average estimate
from the two southwestern demographic studies.
When partitioned by forest type, analysis of
these data by the Team showed significantly
higher densities (F = 16.93, df = 2, P = 0.0001)
in the mixed-conifer (x = 0.275 owls/km 2 ,
SE = 0.046 [0.704 owls/mi 2 , SE = 0.117]) compared
to the pine-dominated (x = 0.080
owls/km 2 , SE = 0.028 [0.204 owls/mi 2 ,
SE = 0.073]) and pinyon-juniper habitats
(x = 0.022 owls/km 2 , SE = 0.036 [0.056 owls/
mi 2 , SE = 0.038]). Density was not statistically
different between the latter two forest types
(Figure 1.3b). Forest type explained 69.3% of
the variation in owl density using this ANOVA
model. Skaggs and Raitt (1988) showed similar
results using density of sites rather than owl
density.
Volume II/Chapter 1
CONCLUSIONS
CONCLUSIONS
CONCLUSIONS
The Mexican spotted owl currently occupies
a broad geographic area, but it does not occur
uniformly throughout its range. Instead, the owl
occurs in disjunct localities that correspond to
isolated mountain systems and canyons. This
distribution mimics most historical locations,
with a few exceptions. The owl has not been
reported along major riparian corridors in
12
Mexican Spotted Owl Recovery Plan
Arizona and New Mexico where it historically
occurred, nor in historically-documented areas
of southern Mexico. Riparian communities and
previously occupied localities in the southwestern
United States and southern Mexico have
undergone significant habitat alteration since the
historical sightings (USDI 1994). However, the
amount of effort devoted to surveying these areas
is poorly known and future surveys may document
spotted owls. Surveys conducted to relocate
spotted owls have been unsuccessful in
northern Colorado near Fort Collins and Boulder,
where records exist from the early 1970s and
1980s, and in the Book Cliffs of east-central
Utah where owls were recorded in 1958.
The majority of Mexican spotted owls
currently known to exist occur in the Upper Gila
Mountains Recovery Unit. This unit can be
considered a critical nucleus for the subspecies
because of its central location within the owl’s
range and its seemingly high density of owls.
Other areas likely to be important include the
Sky-islands of southeastern Arizona and the
Sacramento Mountains, New Mexico (Basin and
Range RUs). Throughout its range, most (91%)
Mexican spotted owls occur on public land
administered by the FS.
Density estimates of Mexican spotted owls
contrasted among forest types in the Sacramento
Mountains and between two areas in the Upper
Gila Mountains RU suggest that mixed-conifer
supports more owls compared to pine-oak, pine,
and pinyon-juniper forest types. Mexican spotted
owl densities reported from three areas are
similar to those reported for California spotted
owls occurring in the San Bernardino Mountains,
California and slightly less than the density
of northern spotted owls occurring in
northwestern California.
Limited information inhibits reliable estimation
of the absolute number of Mexican spotted
owls. However, it is apparent from current
patterns in distribution and habitat use that the
subspecies is rare relative to other raptors and is
distributed discontinuously throughout its
range. Species existing under such conditions are
considered vulnerable to extirpation (see
Dawson et al. 1987 for discussion relevant to
spotted owls). Although future efforts will
undoubtedly discover additional owls, the extent

and total number of this subspecies in the
United States will likely not change in magnitude
enough to alter this conclusion. The contrary
is true for Mexico where planned surveys
have begun only recently.
Consequently, current strategies developed
to conserve Mexican spotted owls will be
limited to basic knowledge about the owl’s
distribution. More specific recommendations
will require additional information on the total
population size, population structure, or interactions
among subpopulations.
Volume II/Chapter 1
LITERATURE LITERATURE CITED
CITED
Behle, W. H. 1960. The birds of southeastern
Utah. Univ. Utah Biol. Surv. 12:1-56.
–—. 1981. The birds of Northeastern Utah.
Occas. Publ. No. 2, Utah Mus. of Nat. Hist.,
Univ. of Utah. Salt Lake City, Utah. 136pp.
Bendire, C. E. 1892. Life histories of North
American birds. U.S. Nat. Mus. Spec. Bull. 1.
Blakesley, J. B., A. B. Franklin, and R. J.
Gutiérrez. 1992. Spotted owl roost and nest
site selection in northwestern California. J.
Wildl. Manage. 56:388-392.
Caughley, G. 1977. Analysis of vertebrate
populations. John Wiley and Sons, London,
England. 234pp.
Cirett-Galan, J. M., and E. R. Diaz. 1993.
Estatus y distribucion del buho manchado
Mexicano (Strix occidentalis lucida) en Sonora,
Mexico. Centro Ecológico de Sonora. 66pp.
Dawson, W. R., J. D. Ligon, J. R. Murphy, J. P.
Myers, D. Simberloff, and J. Verner. 1987.
Report of the scientific advisory panel on the
spotted owl. Condor 89:205-229.
Duncan, R. B., S. M. Speich, and J. D. Taiz.
1993. Banding and blood sampling study of
Mexican spotted owls in southeastern Arizona.
Annual report submitted to Coronado Nat.
For., Tucson, Ariz. 21pp.
Enriquez-Rocha, P., J. L. Rangel-Salazar, and D.
W. Holt. 1993. Presence and distribution of
Mexican owls: a review. J. Raptor Res.
27:154-160.
Fletcher, K. W. 1990. Habitats used, abundance
and distribution of the Mexican spotted owl,
Strix occidentalis lucida, on National Forest
13
Mexican Spotted Owl Recovery Plan
system lands. U.S. For. Serv., Southwestern
Region, Albuquerque, N.M. 55pp.
Forsman, E. D., E. C. Meslow, and M. J. Strub.
1977. Spotted owl abundance in young versus
old-growth forests, Oregon. Wildl. Soc. Bull.
5:43-47.
Forsman, E. D., C. R. Bruce, M. A. Walter, and
E. C. Meslow. 1987. A current assessment of
the spotted owl population in Oregon.
Murrelet 68:51-54.
Franklin, A. B., J. P. Ward, R. J. Gutiérrez, and
G. I. Gould, Jr. 1990. Density of northern
spotted owls in northwestern California. J.
Wildl. Manage. 54:1-10.
Ganey, J. L., and R. P. Balda. 1989. Distribution
and habitat use of Mexican spotted owls in
Arizona. Condor 91:355-361.
Gutiérrez, R. J., D. R. Olson, and M. E.
Seamans. 1994. Demography of two Mexican
spotted owl populations in Arizona and New
Mexico. Report submitted to Humboldt State
Univ. Foundation, Arcata, Calif. 29pp.
Huey, L. M. 1930. Notes from the vicinity of
San Francisco Mountain, Arizona. Condor
32:128.
Johnson, J. A., and T. H. Johnson. 1985. The
status of the spotted owl in northern New
Mexico. New Mexico Dept. Game and Fish,
Sante Fe, N.M. 39pp.
Kertell, K. 1977. The spotted owl at Zion
National Park, Utah. West. Birds 8:147-150.
LaHaye, W. S., and R. J. Gutiérrez. 1994. Big
Bear spotted owl study, 1993. Report
submitted to Calif. Dept. of Fish and Game,
Non-game Bird and Mammal Wildl. Manage.
Div., Sacramento, Calif. 12pp.
Ligon, J. S. 1926. Habits of the spotted owl
(Syrnium occidentalis). Auk 43:421-429.
McDonald, C. B., J. Anderson, J. C. Lewis, R.
Mesta, A. Ratzlaff, T. J. Tibbitts, and S. O.
Williams. 1991. Mexican spotted owl (Strix
occidentalis lucida) status report. U.S. Fish and
Wildl. Serv., Albuquerque, N.M. 85pp.
Olson, D. R., M. E. Seamans, and R. J.
Gutiérrez. 1993. Demography of two
Mexican spotted owl (Strix occidentalis lucida)
populations in Arizona and New Mexico:
preliminary results, 1992. Humboldt State
Univ., Arcata, Calif.

Phillips, A. R., J. T. Marshall, Jr., and G.
Monson. 1964. The birds of Arizona. Univ. of
Ariz. Press., Tucson, Ariz.
Reynolds, R. T., 1989. Preliminary survey of the
distribution and habitat of Mexican spotted
owls in Colorado. U.S. For. Serv. Rocky Mtn.
For. and Range Exp. Stn., Laramie, Wyo.
19pp.
——., and C. L. Johnson. 1994. Distribution
and ecology of the Mexican spotted owl in
Colorado: annual report. U.S. For. Serv.
Rocky Mtn. For. and Range Exp. Stn., Ft.
Collins, Colo. 14pp.
Rinkevich, S. E. 1991. Distribution and habitat
characteristics of Mexican spotted owls in
Zion National Park, Utah. M.S. Thesis,
Humboldt State Univ., Arcata, Calif. 62pp.
Seamans, M. E., D. R. Olson, and R. J.
Gutiérrez. 1993. Demography of two
Mexican spotted owl (Strix occidentalis lucida)
populations in Arizona and New Mexico:
preliminary results, 1992. Humboldt State
Univ., Arcata, Calif.
Skaggs, R. W., 1988. Status of the Spotted Owl
in southern New Mexico: 1900-1987. New
Mexico Dept. Game and Fish, Sante Fe, N.M.
——., and R. J. Raitt. 1988. A spotted owl
inventory of the Lincoln National Forest,
Sacramento Division, 1988. New Mexico
Dept. Game and Fish, Sante Fe, N.M. 12pp.
Tanner, J. T. 1978. Guide to the study of animal
populations. Univ. Tennessee Press, Knoxville,
Tenn. 186pp.
Volume II/Chapter 1
14
Mexican Spotted Owl Recovery Plan
Thomas, J. W., E. D. Forsman, J. B. Lint, E. C.
Meslow, B. R. Noon, and J. Verner. 1990. A
conservation strategy for the spotted owl. U.S.
Gov. Print. Off., Washington, D.C. 427pp.
USDA Forest Service. 1990. Management
guidelines and inventory and monitoring
protocols for the Mexican spotted owl in the
Southwest Region. Federal Register
55:27278-27287.
USDI. 1994. The impact of federal programs on
wetlands. Vol II., A report to Congress by the
Secretary of the Interior. U. S. Dept. of
Interior, Washington, D.C.
Ward, J. P., Jr., A. B. Franklin, and R. J.
Gutiérrez. 1991. Using search time and
regression to estimate abundance of territorial
spotted owls. Ecol. Applic. 1:207-214.
Webb, B. 1983. Distribution and nesting requirements
of montane forest owls in Colo
rado. Part IV: spotted owl (Strix occidentalis).
Colo. Field Ornithol. 17:2-8.
White, G.C., A. Franklin, and J.P. Ward, Jr.,
1995. Population biology. Pages ___ - __ in
Recovery plan for the Mexican spotted owl.
Vol. . USDI, U.S. Fish and Wildl. Serv.,
Albuquerque, N.M.
Williams, S. O., III, and R. W. Skaggs. 1993.
Distribution of the Mexican spotted owl (Strix
occidentalis lucida) in Mexico. Unpubl. Tech.
Rep., New Mexico Dept. Game and Fish,
Sante Fe, New Mexico. 38pp.

The development of recovery guidelines
and criteria for Mexican spotted owl populations
requires understanding the life history traits and
population processes for this species. We examined
the characteristics and trends of Mexican
spotted owl populations at three spatial scales:
range-wide, regional, and local. Range-wide
scales correspond to characteristics and processes
occurring across the U.S. geographic range of
the subspecies. Regional scales correspond to
recovery units that were delineated according to
broad ecological patterns (see Rinkevich et al.
1995). Local scales roughly correspond to
subpopulations that occur within each recovery
unit. Ideally, the same population characteristics
and processes should be examined over different
temporal and spatial scales. However, temporal
comparisons were restricted because historical
information on Mexican spotted owl populations
does not exist. Thus, we could not compare
historical and current populations to assess the
impacts of past and present management activities.
In this section, we first review the sources
of information available for making inferences
about Mexican spotted owl populations. We
then quantitatively describe the life history
characteristics of the owl using age- and sexspecific
survival probabilities and fecundity rates.
These characteristics were estimated from data
collected during radio-telemetry studies, banding
studies, and a regional FS monitoring program.
We examined population trends first by estimating
the finite rate of population change (l) on a
local scale using our estimates of survival and
fecundity from selected studies and then by
evaluating temporal trends in occupancy rates of
FS management territories (MTs) on a regional
scale. Finally, we attempted to examine relationships
of vegetation type on reproductive output
at a range-wide scale. Through this stepwise
procedure, we evaluated the current state of
Mexican spotted owl populations.
Volume II/Chapter 2
CHAPTER CHAPTER 2: 2: Population Population Biology
Biology
Gary C. White, Alan B. Franklin,
and James P. Ward, Jr.
1
Mexican Spotted Owl Recovery Plan
SOURCES SOURCES OF OF INFORMATION
INFORMATION
Since 1989, organized surveys for Mexican
spotted owls have been conducted by personnel
of the FS, BLM, NPS, Tribes, State wildlife
agencies, and by private researchers. Most
surveys followed the procedures described for the
FS Region 3 (USDA Forest Service 1990).
Under the FS Region 3 system, two types of
surveys, inventory and monitoring, were conducted
for different purposes. Inventories were
general surveys used to detect the presence of
spotted owls within a defined area. Monitoring
specifically assessed temporal changes in site
occupancy and reproduction by spotted owls in
management territories (MT). Both procedures
required adherence to a standard survey protocol.
In addition, two types of monitoring,
“formal” and “informal,” were utilized, with
formal monitoring following guidelines of
USDA Forest Service (1990). MTs were monitored
each year from 1989 through 1993 with
the formal procedures if they had (1) no previous
management activity, (2) activity
5-20 years prior to monitoring, or (3) recent
activity within 5 years of monitoring. Formal
monitoring resulted in more survey effort per
MT than for informal monitoring (although
some informal monitoring sites were visited
more often than required by formal monitoring).
Informal monitoring could be conducted at
any site not formally monitored in any year. The
greatest amount of effort for surveys was devoted
to formal monitoring, followed by informal
monitoring, and then inventory.
A limitation of the FS database was that the
MTs surveyed were not randomly sampled from
all possible MTs. MTs were added to the database
as owls were found. We do not expect
excessive bias in estimated fecundity or persistence
(as defined in Life History Parameters
section) from this nonrandom sample because
these parameters are probably not directly linked
to the sample selection procedures. We do expect

significant biases in the estimates of density,
abundance, and occupancy rate because including
an MT in the sample is directly linked to
these parameters.
In 1990, a study of Mexican spotted owl
population dynamics was initiated in the Sky
Islands of southeastern Arizona (Duncan et al.
1993). This study complemented inventory and
monitoring efforts on the Coronado National
Forest. In 1991, two other studies on population
dynamics were initiated: one on the Coconino
National Forest in northern Arizona (Gutiérrez
et al. 1993, 1994) and the other on the Gila
National Forest in west-central New Mexico
(Gutiérrez et al. 1993, 1994). These two studies
were conducted independently from inventory
and monitoring efforts, and thus used methods
different than the formal monitoring protocol.
In all three population studies, owls were located,
captured, individually marked for future
recognition, and the number of fledged young
were recorded. These population studies offer
the most reliable information currently available
for estimating abundance, rates of reproduction
and survival, and for deriving short-term estimates
of population change. However, inferences
from these studies are somewhat limited because
their study areas were not randomly selected
from a defined sampling frame. Even with this
limitation, estimates from these studies are useful
in our preliminary evaluation of Mexican spotted
owl population biology.
Most inventory and monitoring work was
conducted by personnel of the FS Region 3. By
direction (Forest Service Manual 2676.2), survey
data were recorded on standard forms and maps
following field observations. MTs were assigned
using the survey results. Occupancy and reproductive
status of Mexican spotted owls were
summarized by MT at the close of each fiscal
year (30 September). These summaries did not
include all information recorded on field forms,
such as that used to determine occupancy,
reproductive status, or spatial coordinates of owl
locations. Original data recorded on field forms
were necessary for verifying occupancy and
reproductive status. Without this type of verification,
reliability of previous assignments cannot
be demonstrated. Further, spatial coordinates
compatible with a Geographic Information
Volume II/Chapter 2
2
Mexican Spotted Owl Recovery Plan
System (GIS) were required to document owl
distribution and conduct habitat analyses at
various spatial scales. Unfortunately, the original
data and GIS-compatible coordinates were not
entered into a computerized database. Thus, the
Team attempted to compile and create its own
database (referred to as the Team database) from
original data forms and plotted locations to
supplement summaries provided by the FS
Region 3 Office (referred to as the FS database).
Attempts to create the Team database met
with limited success. Entering a portion of the
data forms by a professional data-entry service
failed because standard codes and recording
instructions were not followed by data collectors.
Further, various details were not recorded and
maps were missing. In a second attempt, the
Team formed and trained a set of crews to visit
FS Ranger Stations and Supervisor Offices to
enter data from forms and maps and to record
Universal Transverse Mercator (UTM) coordinates
of owl locations associated with surveys.
The same information was collected from land
management agencies throughout the owl’s
range for the four-year period (1990-1993).
Year-end summaries from the FS Region 3 were
compared to output from the Team database to
verify similarity for the period 1990-1993.
We found many discrepancies between the
Team and FS Region 3 databases, the greatest
being fewer territories with complete reproductive
information in the Team’s database. The FS
database contained 1,984 records, whereas the
Team’s database contained only 377 observations
where valid estimates of reproductive output
(number of fledged young) were available. A
valid estimate of reproductive output was one for
which appropriate protocols (see Forsman 1983,
USDA Forest Service 1990) substantiated the
estimate or for which young were reported.
Thus, we were able to locate only a fraction of
the data presumably available.
When the two databases were merged, we
found 11 records in the Team database that had
no corresponding record in the FS database.
Further, the FS database has no fecundity
estimate for 45 records for which the Team’s
database had a valid fecundity estimate. Of the
321 records that matched, 271 records had
identical values for reproductive output. Eight of

the remaining records had greater values in the
Team database, whereas 42 had greater values in
the FS database. For the 321 matching records,
the FS database had a significantly greater
fledgling rate (P < 0.001) than the Team database.
The expected bias was that the FS database
would have a lower estimate of reproductive
output because many of the records with zero
young reported were not properly substantiated
by mousing data as was done in the Team
database. However, changes by the FS occurred
during summarization procedures, among them
selected territories with zero young recorded
were changed to unconfirmed (Keith Fletcher,
FS, Albuquerque, NM, pers. comm.). Therefore,
the FS database has a higher estimate of reproductive
output because a number of territories
with valid values of zero were eliminated from
the calculation. This would introduce an overestimate
of reproductive output. Whether the two
biases in the FS database cancel each other is
unknown.
A potential problem with the Team database
was the incomplete availability of data
forms; many of the needed forms were missing.
The last form used to complete the estimate of
reproduction for many of the MTs may not have
been available for data entry. As a result, the
Team database has a lower estimate of reproduction
than the FS database. The Team’s effort to
validate the FS estimates of fecundity does not
accomplish this objective. Rather, the Team
database appears too incomplete to be useful for
estimating fecundity. Therefore, we have used
estimates of fecundity from the FS database with
the understanding that these estimates may be
biased for two reasons: inadequate validation of
the fecundity and occupancy results, and nonrandom
sampling. The benefit of the Team
obtaining raw data from the FS is that this effort
has demonstrated severe problems with the
handling of data collection, data management,
and data analysis for the monitoring program.
By discovering these problems, the problems are
correctable in the future.
Volume II/Chapter 2
3
Mexican Spotted Owl Recovery Plan
LIFE LIFE HISTORY HISTORY PARAMETERS
PARAMETERS
PARAMETERS
An organism’s life history is the combination
of birth and death processes exhibited in its
natural environment (Partridge and Sibley
1991). The optimal trade-off in survival and
reproduction, resulting in fitness, should be
maximized by the life history favored by natural
selection. Under optimality theory, the
organism’s life history is a finely tuned result of
adaptations to its environment; major perturbations
to an organism’s environment could
eventually lead to its extinction. However,
behavioral plasticity may allow organisms to
adjust life-history strategies to current environmental
conditions (Hansen and Urban 1992).
When examining recovery of a species after past
and present environmental perturbations of
varying magnitudes, one must question whether
that species will perish or persist. Therefore,
examining the life history characteristics of the
Mexican spotted owl is paramount to understanding
how it responds to changes in its
environment.
An organism’s life history can be quantitatively
described in terms of age- and sex-specific
survival, age- and sex-specific fecundity rates,
longevity, and age at first reproduction (Stearns
1992). In the following section, we outline
current estimates of life history parameters for
the Mexican spotted owl, using a variety of
estimators calculated with different sources of
data. These parameters can be used in two ways
to make inferences about Mexican spotted owl
populations: (1) to estimate the finite rate of
population change (l), and (2) to examine
components of fitness within populations (Roff
1992).
Age- Age- Age- and and Sex-Specific Sex-Specific Sex-Specific Survival
Survival
We estimated age- and sex-specific survival
for Mexican spotted owls using mark-recapture
estimators with data from banded owls in
population studies, binomial survival estimators
with data from radio-tagged owls studied at
various locations, and survival estimators from
data collected during the FS monitoring program.
Where feasible, we recognized four age

classes: juveniles (J), first-year subadults (S1),
second-year subadults (S2) and adults (A), all as
described by Forsman (1981) and Moen et al.
(1991). Juveniles (age, x = 0 years) were fledged
young-of-the-year. First-year subadults (x = 1
year), second-year subadults (x = 2 years), and
adults (x ³ 3 years) have similar body plumage
but were distinguished by different retrix characteristics
(Moen et al. 1991). Not all studies
differentiated the two subadult age classes, so
these two age classes were usually lumped into a
single subadult (S) age class for the purpose of
estimating survival. We distinguished between
subadults and adults because subadults usually
have lower reproductive rates than adults.
Mark-recapture Mark-recapture Survival Survival Estimators Estimators from
from
Population Population Population Studies Studies
Studies
Mark-recapture estimators yield maximum
likelihood estimates of apparent survival (f) and
recapture (or resighting) probability (p), which
are asymptotically unbiased, normally
distributed, and have minimum variance
(Lebreton et al. 1992). An important
consideration with apparent survival is that
1- f = death + permanent emigration. For
apparent survival to accurately reflect true
survival (S), permanent emigration over the
course of the study must be close to zero. Emigration
is difficult to quantify, requiring the use
of large samples of radio-marked birds.
Another limitation of the mark-recapture
data is that only territorial birds are marked,
because nonterritorial birds (“floaters”) do not
respond to the capture and sighting methods
employed. Even though marked juveniles enter
the floater population, they are not recaptured
until they become territorial, which may not
happen because they emigrate from the study
area. Floaters that never become territorial are
never included in the data to estimate survival,
even if they remain on the study area. As a result,
juvenile and subadult survival estimates produced
from birds banded as juveniles are biased
low because of the entry into the floater population
and/or emigration from the study area.
However, estimates of survival generated from
subadults and adults marked as territorial birds,
hence with negligible emigration, are unbiased if
Volume II/Chapter 2
4
Mexican Spotted Owl Recovery Plan
inference is only to territorial birds. Thus,
inferences from the mark-recapture data only
apply to the territorial population because only
birds from the territorial population are marked.
We examined mark-recapture data from
color-banded Mexican spotted owls derived from
the three population study areas (Figure 2.1):
(1) a 484-km 2 (187-mi 2 ) area located on the
Coconino National Forest (Upper Gila Mountains
RU) denoted as the CSA (Gutiérrez et al.
1994); (2) a 323-km 2 (125-mi 2 ) area located on
the Gila National Forest (Upper Gila Mountains
RU) denoted as the GSA (Gutiérrez et al. 1993);
and (3) an area encompassing portions of the
Sky Island Mountains in southeastern Arizona
(Basin and Range - West RU) denoted as the
SISA (Duncan et al. 1993). A total of 148 adult,
44 subadult, and 238 juvenile capture histories
compiled during 3- and 4-year periods were
utilized in the subsequent analyses (Table 2.1).
Methods used to estimate survival from the
mark-recapture data are detailed in Burnham et
al. (1994) and Lebreton et al. (1992). Two sets of
parameters are estimated with these models: f is
the probability of a bird remaining alive and on
the study area, and p is the probability that the
bird will be resighted after initial capture. Both f
and p are indexed to provide specific estimates
with respect to time, age, sex, and area. We
employed three analyses: (1) goodness-of-fit
testing to the Cormack-Jolly-Seber (CJS) models
using computer program RELEASE (Burnham
et al. 1987) and JOLLY (Pollock et al. 1990); (2)
examination of a wide variety of models progressing
from a biologically realistic global model
to the simplest model using program SURGE
(Lebreton et al. 1992); and (3) selection of the
most parsimonious model with Akaike’s Information
Criteria (AIC) and likelihood ratio tests
(LRT) (Lebreton et al. 1992).
Goodness-of-fit tests of data to the CJS
model include Test 2, which tests primarily for
lack of independence, and Test 3, which primarily
tests for heterogeneity in survival and recapture
probabilities (Burnham et al. 1987). We
could only use Test 2 because of the short
duration of the studies. Test 2 of the GSA and
SISA data did not indicate lack of fit of the data
(GSA: c 2 = 0.008, 1 df, P = 0.93; SISA:
c 2 = 0.702, 1 df, P = 0.40). Test 2 was not

Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Figure Figure 2.1. 2.1. Location of Coconino (CSA), Gila (GSA), and Sky Islands (SISA) Mexican spotted owl
population study areas in Arizona and New Mexico.
FPO
Table Table 2.1. 2.1. Time periods and number of capture histories from three study areas used in estimating
Mexican spotted owl survival.
Age Age Class Class When When B BBanded
B anded
Adults dults
Subadults ubadults
Juv uv uveniles uv eniles
Coconino Coconino S SStudy
S tudy Ar Area Ar ea
(CSA)
(CSA)
1991-1993
Gila ila S SStudy
S tudy Ar Area Ar ea
(GSA)
(GSA)
1991-1993
Sky ky II
Island I sland S SStudy
SS
tudy Ar Area Ar ea
(SISA)
(SISA)
1990-1993
41 52 55
18 15 11
95 84 59
5

computable for the CSA because only one bird
released in 1991 was not recaptured in 1992 but
was captured in 1993.
For model selection, the GSA and CSA
data sets were modeled together because they
employed similar designs and methodologies
(Gutiérrez et al. 1993, 1994), both occur in the
Upper Gila Mountains RU, and we wanted to
improve the precision of survival estimates by
combining the data into one analysis. The
procedures used allowed testing the assumption
that survival and recapture rates were the same
for these two study areas. The SISA data set was
modeled separately from the CSA and GSA data
sets because it was conducted by a separate set of
investigators using somewhat different protocols,
and because this study occurred in the Basin and
Range - West RU. In modeling the GSA and
CSA data, we considered the global model to be
{f g*s*a , p g*s*a } (AIC = 249.05, K = 28 parameters);
it included study area (or group, g), sex (s), and
age (a) effects. We did not include time effects
because only two recapture periods were present
in the data. The selected model
{f J*g ,f S,A(GSA),AM(CSA) , f AF(CSA) , p S1 , p S2,A } (AIC =
223.24, K = 6) included (1) separate estimates of
juvenile (J) survival for each study area, (2) a
single estimate for subadults (S) and adults (A)
of both sexes on the GSA combined with subadults
of both sexes and male adults (AM) on the
CSA, and (3) a single estimate for adult females
(AF) on the CSA. No significant study area
effects in terms of recapture probabilities (p)
were found but there was an age effect (S1 ¹ S2
and A age classes). However, the estimate of f
for CSA females was 1.000 ( se (f) = 0.000),
which was unsuitable for modeling purposes.
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Mexican Spotted Owl Recovery Plan
Other than indicating that adult females may
^
have higher survival than males, the f for adult
females on the CSA was probably an artifact of
limited number of capture occasions. Such a
result is possible from a study with only three
capture occasions. Therefore, we used the nearest
model to the selected model; i.e., the model
with the next lowest AIC. This model {f , f , J*g A,S
p , p } (AIC = 229.53,
S1 A,S2
K = 5) included separate estimates of juvenile
survival for the two study areas and a single
estimate for subadults and adults, with no sex
effects (Table 2.2). Recapture probabilities were
modeled the same as the previous model.
Estimated differences in juvenile survival
between the two study areas may represent
differences in survey effort around the study
areas and differences in study area size rather
than real differences in the rates. For more
explanatory details, refer to the Population
Trends section.
We could not obtain reliable estimates from
the SISA. For all the preliminary models examined,
survival estimates became bounded at the
upper limit of 1 indicating problems with the
estimation procedure. The selected model (f, p)
^
had a single survival estimate (f = 1.0000,
se ^ ^
(f) = 0.0000) and a single estimate of recapture
probability (p ^ = 0.2366, se ^ ^ (p) = 0.0344)
with no age, sex, or time effects on either estimate.
Such a conclusion is not biologically
realistic; and given that the protocol used in this
study did not stress resighting of marked birds
(as evidenced by the low estimate of p), we do
not feel these results are useful.
Table Table 2.2. 2.2. Apparent survival (f), recapture probability (p), and their sampling standard errors
estimated for Mexican spotted owls between 1991 and 1993 on the Gila Study Area (GSA), New
Mexico, and the Coconino Study Area (CSA), Arizona.
Age-class Age-class (S (Study (S tudy ar area) ar ea)
Juv uv uv uvenile uvenile
enile (GSA)
(GSA)
Juv uv uvenile uv enile (CSA)
(CSA)
^ ^
^ ^ ^ ^
^
0.2861
se se ( (f) (
0.0366
0.0785
Subadult ubadult & & A AAdult
A dult (GSA (GSA & & CSA)
CSA) 0.8889 0.0269 0.9818
aRecapture probabilities for juveniles represent probability of recapture as an S1 or S2 individual.
f
0.0643
6
p
0.7147 a
0.7147 a
^ se se ( (p) (
0.1524
0.1524
0.0176

Binomial Binomial Survival Survival Estimators Estimators from
from
Radio-tracking Radio-tracking Studies
Studies
Binomial estimators allow estimation of
true survival (S) where 1 - S = mortality. Estimates
of S can be derived from radio-telemetry
data and are preferable to estimates of apparent
survival when permanent emigration occurs,
radios do not influence survival, and sufficient
numbers of radios are available for precise
estimates. We estimated annual survival for
subadult and adult Mexican spotted owls based
on 73 radio-marked individuals from six studies
at four geographic locations (Table 2.3). We also
used 22 juveniles from two independent studies,
one in Colorado (R. Reynolds, unpub. data) and
one in Utah (Willey 1992a, b). We selected the
Kaplan-Meier product limit estimator (Kaplan
and Meier 1958) as modified by Pollock et al.
(1989) to analyze the radio-telemetry data. This
estimator allowed for staggered entry of individuals
during the sampling period and the use
of right-censored data (exact fates of individuals
unknown due to radio failure) without incurring
the biases due to censoring discussed by White
and Garrott (1990). In addition, this estimator is
nonparametric and, therefore, does not require
an underlying hazard function that must be
mathematically tractable (Pollock et al. 1989).
Five important assumptions underlie the
Kaplan-Meier estimator: (1) individuals have
been randomly sampled; (2) survival of the
marked animal is independent of other individuals;
(3) attached radios do not influence survival;
(4) censoring is random and unrelated to an
individual’s fate; and (5) newly marked individuals
have the same survival rate as previously
marked individuals. We were unable to test these
assumptions because of low sample sizes and
design of the studies. However, we felt that
assumption (1) was probably not met because of
the nature of the studies whereas assumptions
(2)-(5) probably were met. However, controversy
exists whether radios and their attachment
(assumption 3) affect survival (Paton et al. 1991,
Foster et al. 1992), although the studies reported
here used tail-mounted radios rather than the
backpacks discussed by the references. This
assumption cannot be tested with just radiotracking
data.
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7
Mexican Spotted Owl Recovery Plan
Adult and subadult age classes were pooled
for analyses because of the small sample of
subadults in the radio-marked samples and for
comparability with the mark-recapture estimates.
Sex-specific estimates of adult and subadult
survival were computed by pooling data across
study areas. Pooling across study areas was
necessary because of low sample sizes within
each study area. In addition, data on both sexes
from the Coconino National Forest were combined
for comparison with the mark-recapture
estimates from the CSA population study on
that forest. The pooling of data across study
areas and years prevented us from examining
spatial and temporal variation in the Kaplan-
Meier estimates of survival. In all Kaplan-Meier
models, the annual sampling period started on 1
June because most birds were radio-marked just
after this date, this coincided with approximately
the middle of the sampling period for the
population studies, and this was the “birth” date
used for fledglings in population modeling
(Franklin 1992). In all models, individuals
tracked beyond the annual sampling period were
recycled back to the beginning. For example, an
individual that was radio-marked in July and
then had radio failure in August of the following
year would be initially added in July, added again
in the following June, and then censored in
August. In this way, the number of entries in the
model exceeded the actual number of individuals
tagged and the only fates for an individual were
to die or be censored from the analysis.
Estimates of S for adults and subadults
combined were close to identical for both sexes
when study areas were pooled (Table 2.4). On
the Coconino National Forest, Kaplan-Meier (S)
and mark-recapture (f) estimates were compared
for adult/subadult (both sexes combined) and
juvenile age classes using a Wald test (Carroll
and Ruppert 1988, Hosmer and Lemeshow
1989):
c 2
(1) =
^
(S - f) 2
var ^ ^ ^
(S) + var ^ (f)
Estimates from mark-recapture data were
not significantly different from those estimated
from the radio-telemetry data (c 2 = 0.950, 1 df,
P = 0.330). Estimates for juvenile survival from
^

8
Table Table 2.3. 2.3. Description of radio-telemetry studies conducted on adult and subadult Mexican spotted owls in the Upper Gila (Norther AZ, Coconino
NF, AZ), Basin and Range - East (Lincoln NF, NM), Southern Rocky Mountains Colorado (Rocky Mts, CO), and Colorado Plateau (Zion NP, UT)
RUs.
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the radio-telemetry data (Table 2.4) were not
significantly different from estimates from markrecapture
data collected on the CSA (c 2 = 0.752,
1 df, P = 0.386) or the GSA (c 2 = 2.749, 1 df,
P = 0.097).
Survival Survival Estimators Estimators Estimators from from FS FS FS Region Region 3
3
Monitoring Monitoring Studies
Studies
The FS has inventoried Mexican spotted
owl MTs since 1984, and conducted informal
and formal monitoring since 1989 (Table 2.5).
Summaries of monitoring data were supplied by
the FS (see Sources of Information section). For
each MT, presence of owls (single male, single
female, single unknown, unknown age and sex,
or pair, or else unchecked) and result of reproduction
(0, 1, 2, 3 young, unchecked, or unconfirmed)
were noted.
Persistence of a pair can be estimated from
occupancy data gathered during the FS spotted
owl monitoring program. Pair persistence rate is
defined here as the probability that a territory
containing a pair of owls in one year will contain
a pair in the succeeding year (but see discussion
of biases below). An individual territory must be
monitored both years to compute this statistic.
The overall persistence rate was 80.5% for 824
territories monitored with formal and informal
protocols (Table 2.6). Note that some territories
had persistence estimates for their first year
because some of these MTs were surveyed as part
of inventory the preceding year. No differences
in the persistence rate across years were detected
for the informal monitoring data (1989-1993;
c 2 = 2.543, 4 df, P = 0.637), or the formal
monitoring data (1989-1993; c 2 = 3.233, 4 df,
P = 0.520). We found no significant differences
for year (c 2 = 4.2546, 4 df, P = 0.373), monitoring
type (c 2 = 0.7133, 1 df, P = 0.398), or their
interaction (c 2 = 1.3162, 4 df, P = 0.859) using
a logistic regression model (Hosmer and
Lemeshow 1989).
The overall persistence rate based on pairs
versus no pairs from 1989-1993 formal and
informal monitoring types (0.805, SE = 0.0138)
was used to estimate adult survival (S a ). If pairs
are assumed to remain on the same territory, lack
of a pair on a territory that was previously
occupied infers the death of one or both members
of the pair. This is a difficult assumption to
accept because pairs have been observed to
change nest locations, but it allows some inference
about adult survival. The dichotomy of
pairs versus no pairs was used because this
assumption is the simplest one possible for
estimating survival from persistence. Single birds
(i.e., persistence of a single) could be included in
the analysis to estimate survival, but would
require an assumption that single males persisted
on the territory at the same rate as single females.
Another bias is failure to detect a pair
when both birds are present. Using the dichotomy
of pairs versus no pairs, and assuming
Table Table 2.4. 2.4. Estimates of true survival (S) for Mexican spotted owls based on radio-telemetry
data.
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9
Mexican Spotted Owl Recovery Plan

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Mexican Spotted Owl Recovery Plan
Table Table 2.5. 2.5. Number of management territories checked one or more times during the Mexican
spotted owl monitoring program of FS Region 3.
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Table Table 2.6. 2.6. Persistence of a Mexican spotted owl pair on a territory for formal and informal monitoring
data, with “persistence” defined as the probability a pair of owls will exist on a territory given
that a pair was on the same territory the previous year. Data are from the monitoring program of FS
Region 3.
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10

that both adults survive at the same rate and
independent of one another, then (S ) a 2 ^
= 0.805,
^ ^ ^
or S = 0.897 (se (S ) = 0.0077). This estimate is
a a
very close to the observed estimate of apparent
survival from the population studies (0.889).
Two biases of opposite direction are possible
for an estimate of adult survival based on
pair persistence. A pair of owls may leave a
territory for reasons other than the death of one
member of the pair, resulting in an estimate of
survival biased low. In contrast, one member of a
pair may die, but the remaining member may be
able to obtain another mate and stay on the
territory. Another possibility is that both members
of a pair die, but the territory is occupied by
a new pair. In these situations, the estimate of
survival is biased high. For this reason, we note
the similarity of persistence-based survival (S a ) to
mark-recapture estimates (f) but we relied solely
on the mark-recapture estimates to estimate
population trends.
The 1989-1993 formal and informal
persistence data were also analyzed by recovery
unit (Table 2.7) using a logistic regression model
that included year (1989-93), recovery unit and
the interaction between the two factors. No
differences were found for year (c 2 = 5.9688,
4 df, P = 0.202), recovery unit (c 2 = 2.6129,
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^
^
Mexican Spotted Owl Recovery Plan
4 df, P = 0.624), or the interaction between the
two (c 2 = 13.1995, 15 df, P = 0.587). Therefore,
a reduced model with only recovery unit was
analyzed; and again, no differences were found
for recovery unit (c 2 = 7.0271, 4 df, P = 0.134).
Survival Survival Estimates Estimates from from Band Band Return Return Data
Data
Records from the FWS Banding Laboratory
were checked to determine if adequate banding
data were available for estimation of survival. All
records obtained from the Laboratory were part
of studies reported above, so did not provide
additional information.
Age- Age- and and Sex-specific Sex-specific Sex-specific Fecundity
Fecundity
Fecundity (m x ) can be defined as the mean
annual number of live births of a given sex by a
parent of that same sex over an interval of age
(Caughley 1977), e.g., the number of female
young per adult female. For Mexican spotted
owls, we defined live births as the number of
young fledging from the nest because the number
of live births at hatching was not measured.
To estimate fecundity, we initially used the
number of total young (e.g. of both sexes)
fledged per pair as the response variable from the
Table Table 2.7. 2.7. Persistence of a pair of Mexican spotted owls on a territory for the five recovery units
contained in the FS Region 3 monitoring database for 1989-1993, with “persistence” defined as the
probability a pair of owls will exist on a territory given that a pair was on the same territory the previous
year. Survival rate is the probability that both members of the pair survived the year, and is the
square root of persistence.
FPO
11

two appropriate population studies (GSA and
CSA) and the FS monitoring database. The
third population study (SISA) was included in
the analysis of the FS monitoring database
because the methods used and territories monitored
were identical. We analyzed the two
population studies separately from the monitoring
database to obtain fecundity estimates
directly related to the mark-recapture estimates
of survival. Estimates for number of young
fledged were converted into fecundities by
dividing the means in half and adjusting the
standard errors accordingly. This procedure
assumed a 1:1 sex ratio at fledging and that sites
where reproductive data were gathered were
independent across years.
Fecundity Fecundity Estimates Estimates Estimates from from Population Population Population Studies
Studies
We used the general linear models procedure
in SAS (PROC GLM; SAS Institute Inc.
1985) to examine differences in time, age, and
study areas for number of young fledged by male
and female Mexican spotted owls. Average
number of young fledged for all years differed
between the GSA and CSA (F = 3.73; 1, 151 df;
P = 0.055) but average number of young per
year for combined study areas did not differ
among years of study (F = 1.58; 2, 151 df;
P = 0.210). Based on a priori linear contrasts,
number of young fledged by first-year subadults
was different from second-year subadults and
adults combined for both males (F = 3.45; 1,
151 df; P = 0.065) and females (F = 16.24; 1,
151 df; P < 0.001; Table 2.8).
Fecundity Fecundity Estimates Estimates from from FS FS Region Region 3
3
Monitoring Monitoring Database
Database
An objective of the FS Region 3 monitoring
program was to monitor reproduction (Table
2.9). Differences in mean reproduction across
monitoring methods and years were tested with
analysis of variance (ANOVA). Reproduction is a
categorical variable, because only values of 0, 1,
2, and 3 young are observed. However, ANOVA
techniques are still appropriate because of the
large sample sizes involved (even though sample
sizes are unequal); and hence, the cell means
being approximately normally distributed as a
Volume II/Chapter 2
12
Mexican Spotted Owl Recovery Plan
result. Another possible procedure might be a
log-linear analysis. However, the null hypothesis
of a log-linear model would be that the distributions
are the same, compared to the null hypothesis
of ANOVA that the means are the same.
Thus, a log-linear analysis may reject the null
hypothesis even when the mean fecundity rates
do not differ. We did not use a log-linear analysis
here because we are primarily interested in the
mean rates.
All data for 1989-1993 were used to test for
differences between formal and informal monitoring
types (Table 2.9). The year effect was
significant (F = 14.09; 4, 685 df; P < 0.001), but
monitoring method (F < 0.001; 1, 685 df;
P = 0.956) and the interaction (F = 1.23; 4,
685 df; P = 0.295) were not significant. The
average number of young fledged/pair across
years was 1.006 (n = 695, SE = 0.037), giving a
fecundity estimate of 0.503 (SE = 0.018).
Differences in mean reproduction among
recovery units with years included in the model
was tested for formal and informal monitoring
data for 1989-1993. The year effect was significant
(F = 3.03; 4, 672 df; P = 0.017), as were
recovery unit (F = 12.55; 4, 672 df; P < 0.001),
and their interaction (F = 2.86; 14, 672 df;
P < 0.001). Mean reproductive rates are given in
Table 2.10 for each year and recovery unit, plus
the recovery unit mean across the years 1989-
1993. Reproduction estimates from the FS
monitoring database were compared to estimates
from the population studies (CSA and GSA) for
the same two National Forests, i.e., Coconino
and Gila. The ANOVA model included year
(1991-1993), National Forest (Coconino, Gila),
and monitoring method (population study
versus formal and informal monitoring), plus all
the interactions of these three factors. None of
the factors was significant (P ³ 0.300) except the
interaction between forest and monitoring
method (F = 5.24; 1, 267 df; P = 0.023). Table
2.11 presents the four means that produced this
interaction.
Although the reasons behind this interaction
are unknown, we speculate that two explanations
are possible for this difference. First,
differences in following the monitoring protocols
between personnel in the Coconino and
Gila National Forests may have led to the

13
Table Table 2.8. 2.8. Sample size (n) and estimates (mean and SE) of number of young fledged/pair and fecundity (female young fledged/female) from the GSAa and CSAa Study Areas, 1991-1993.
FPO

observed differences between the population
studies and other monitoring systems. Monitoring
approaches in the population studies are the
same because each was conducted by the same
research group using standardized methods and
experienced personnel. A second possibility is
that the population study areas are not representative
of the surrounding habitat for their respective
forests; and thus, the observed difference is
real and caused by habitat differences on each
forest. Alternatively, monitoring sites may not be
representative of the forest because management
territories were selected because of proposed
timber sales (with better quality owl habitat) or
historical locations (with easy access).
Effects Effects of of Forest Forest Type Type on on Life
Life
History History History Traits
Traits
We examined the effects of forest type on
both reproduction and persistence, which can be
viewed as an indirect measure of survival. We
used two sources of information to examine the
effects of forest type on reproduction: the FS
Region 3 monitoring database and data from
Skaggs and Raitt (1988). For persistence, we
used data from the FS Southwestern Region
monitoring database. These were the only
sources of data available to the Team which
coupled habitat information with data used to
estimate life history traits.
Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Table Table 2.9. 2.9. Number of Mexican spotted owl pairs checked (n), mean, and standard error (SE) for
number of young fledged per pair for 1989-1993, based on formal and informal monitoring methods.
FPO
14
Effects Effects on on Reproduction
Reproduction
Reproduction
The FS Region 3 monitoring database
included for each MT the percent (recorded to
the nearest 25%) of the core area consisting of
the following forest types: mixed conifer, pineoak,
ponderosa pine, pinyon-juniper, oak,
Arizona cypress, sycamore, other riparian, and
unsuitable for owls. We computed the Pearson
correlations (r) between each of these forest type
variables and number of young produced on an
MT for each year, given that a pair of owls was
present. Significant correlations were found for
mixed-conifer (r = -0.131, P < 0.001), pine-oak
r = 0.084, P = 0.011), other riparian (r = 0.062,
P = 0.064), and unsuitable (r = 0.098,
P = 0.003), with none of the remaining variables
significant (P > 0.154). This analysis suggested
that the more mixed-conifer present, the lower
the reproductive rate (a negative correlation),
and the more unsuitable forest type, the greater
the reproductive rate (a positive correlation).
When the forest type variables were used in a
step-wise regression to predict number of young
fledged, mixed-conifer and unsuitable were both
selected (P £ 0.017), while none of the remaining
variables was included (P > 0.150). The
regression explained only a very small amount
(2.3%) of the variation in the number of young
fledged, with the signs of both variables in the
opposite direction of what we expected based on
radio-telemetry studies (Ganey and Dick 1995).

Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Table Table 2.10. 2.10. Number of Mexican spotted owl pairs checked (n), mean, and standard error (SE) for
number of young produced per pair for 1989-1993 by recovery unit, based on formal and informal
monitoring methods.
FPO
Table Table 2.11. 2.11. Sample size (n), mean, and standard error (SE) for the number of Mexican spotted owl
young produced per territory for 1991-1993, based on population studies (CSA and GSAa ) and formal
and informal monitoring methods in the Coconino and Gila National Forests.
FPO
15

When we examined the database to determine
the distribution of territories with mixed-conifer,
we found that 276 territories with 100% mixedconifer
cover occurred in the Basin and Range -
East RU. These 276 territories were 79.3% of
the territories that had 100% mixed-conifer.
However, only 6 territories with

decreasing persistence, and ultimately fitness. As
discussed previously for the fecundity analysis,
the inequitable distribution of mixed conifer
habitat across recovery units makes this analysis
inappropriate.
Conclusions
Conclusions
Environmental conditions may greatly
affect reproduction and/or survival of nestlings
through fledging and to adulthood. However,
adult survival rates appear to be relatively constant
across years, as suggested by high pair
persistence rates. Such life history characteristics
are common for K-selected species, for which
populations remain relatively stable even though
recruitment rates might be highly variable. With
no recruitment, the population only declines at
the rate of 1 minus adult survival, or the adult
mortality rate.
Undoubtedly, long-lived organisms experience
a range of environmental conditions
through time. Conditions that result in simultaneously
low survival and reproduction can lower
average population persistence rates dramatically,
when examined over a period that is short
relative to the organism’s life span. The converse,
simultaneously high survival and reproduction,
that would raise the expected population persistence
dramatically, is also possible. However, the
magnitude of the effect of such a sudden decrease
or increase on average persistence will
naturally decline as the observation of a given
population is extended in time, while the probability
of detecting such events will increase with
observation time. In addition, dispersal among
subpopulations can greatly influence the persistence
of relatively isolated populations (Keitt et
al. 1995). Successful dispersal may also be a rare
and time-dependent event or a density-dependent
event. We currently have little information
on the frequency of immigration and its associated
influence on population persistence. Thus,
reliable conclusions on the persistence of Mexican
spotted owl populations must await additional
study. Without reliable projections on the
owl’s persistence, we can only summarize conclusions
about the owl’s survival and reproduction
based on short-term but current knowledge.
Volume II/Chapter 2
17
Survival
Survival
Mexican Spotted Owl Recovery Plan
Annual survival rates of adult Mexican
spotted owls is ~0.8-0.9 based on short-term
population and radio-tracking studies and
longer-term monitoring studies. These annual
survival estimates can be viewed as the probability
of an individual surviving from one year to
the next or as the proportion of individuals that
will survive from one year to the next. A variety
of different estimators of adult survival using
different types and sets of data gave similar
results. Juvenile survival is considerably lower
(~0.06-0.29) than adult survival. Juvenile survival
also appears more variable spatially, although
this conclusion reflects only two population
study areas and two radio-telemetry studies
spanning two years or less.
We strongly suspect that estimates of
juvenile survival from the population studies are
biased low because of (1) a high likelihood of
permanent dispersal (emigration) from the study
area, especially the smaller GSA, and (2) a lag of
several years before marked juveniles reappear as
territory holders, at which point they are first
detected for recapture. Concerning the first
point, juvenile northern spotted owls have a
high dispersal capability (reviewed in Thomas et
al. 1990). If Mexican spotted owl juveniles have
a similar dispersal capability, we expect that a
substantial portion of marked juveniles will
emigrate from the respective study areas. However,
estimates from the radio-telemetry study
roughly corroborated the low estimates from the
population studies. Biases in the radio-telemetry
estimates of juvenile survival can result if radios
significantly affect their survival. Whether radios
or their attachment affect survival of northern
spotted owls is debatable (Paton et al. 1991,
Foster et al. 1992). Concerning the second
point, Franklin (1992) found a lag of 1-4 years
between the time when juvenile northern
spotted owls were banded and subsequently
recaptured. If this process is similar for Mexican
spotted owls, then the current population studies
may be of insufficient duration to adequately
estimate juvenile survival.
In summary, our survival estimates are
based primarily on studies of insufficient duration
or studies not explicitly designed to estimate

survival. In most cases, the data were too limited
to support or test the assumptions of the estimators
used. However, the age- and sex-specific
estimates of survival calculated here are useful at
this point as qualitative descriptors of the lifehistory
characteristics of Mexican spotted owls.
That is, Mexican spotted owls exhibit high adult
and relatively low juvenile survival. In this
respect, Mexican spotted owl survival probabilities
appear similar to northern (see review in
Burnham et al. 1994) and California spotted
owls (Noon and McKelvey 1992).
Reproduction
Reproduction
Reproductive output of Mexican spotted
owls, defined as the number of young fledged
per pair, varies both spatially and temporally.
Mexican spotted owls may have a higher average
reproductive rate (1.001 fledged young per pair)
than the California (~0.712; Noon and
McKelvey 1992) and the northern spotted owl
(~0.715; Thomas et al. 1990). Both of the other
subspecies exhibit temporal fluctuations in
reproduction similar to the Mexican subspecies.
Effects Effects of of Forest Forest Type
Type
We feel the data collected by Skaggs and
Raitt (1988) were more appropriate for examining
the effects of forest type on reproduction
than our analysis of the monitoring data. Their
study was designed to look at the relationship
between forest type, density and reproduction
whereas the monitoring program was not.
However, the Skaggs and Raitt data lacked
sufficient statistical power to detect differences
in reproductive output between the three forest
types. This problem arose primarily because
significantly fewer spotted owls were found in
the pinyon-juniper and pine forest types than in
mixed-conifer forests (Ward et al. 1995). The
primary problem in using data on forest types
from MTs is that the data are confounded for
making the desired comparisons. Further, the
core delineations were subjective. In addition,
forest types included within MT boundaries may
not have been used by the owls for which the
given MT was established. For these reasons, we
feel that definitive data linking Mexican spotted
Volume II/Chapter 2
18
Mexican Spotted Owl Recovery Plan
owl reproduction and forest type are still lacking,
even at the coarse-grained scale that we examined.
Further, forest type affects more than just
reproduction; so additional data are needed to
evaluate how forest type affects survival, and
ultimately fitness.
POPULATION POPULATION POPULATION TRENDS
TRENDS
We estimated trends in Mexican spotted
owl populations two ways: as the finite rate of
population change, lambda (l), and as trends in
the rate of occupancy of spotted owl territories.
Finite Finite Finite Rate Rate of of Population Population Population Change
Change
Lambda was computed for female Mexican
spotted owls from the age-specific survival and
fecundity rates obtained from two population
study areas, the GSA and CSA (see Life History
Parameters section). Lambda is a useful metric
because it measures both the direction and
magnitude of change in population trends.
Direction of population trends can be characterized
as stationary (l = 1), declining (l < 1) or
increasing (l > 1). The magnitude in change is
expressed as the annual rate of change, R, where
R = l - 1 for a birth-pulse population. From a
population management perspective, the statistical
hypothesis is l < 1 versus the null hypothesis
that the population is either stationary or increasing
(l ³ 1). This is a one-sided test of the
form:
^
1 - l
^
Z = ,
se (l)
where Z is normally distributed with m = 0,
s 2 = 1.
We used a Leslie matrix (Leslie 1945) as
modified by Usher (1972) to compute estimates
of l based solely on the estimates of age-specific
fecundity and survival probabilities obtained
from the two study areas. The form of the matrix
followed Usher (1972):
f 0 m 1 f 1 m 2
f 0 f 1
,

where f 0 = juvenile survival, f 1 = survival for the
subadult and adult age classes combined,
m 1 = S1 fecundity, and m 2 = fecundity for S2
and adult age classes combined. The form of the
matrix assumed a birth-pulse population with a
post-breeding census and a projection interval of
one year (Noon and Sauer 1992). Lambda was
estimated as the dominant eigenvalue associated
with the right eigenvector derived from the
matrix using power analysis (Caswell 1989). The
se(l) was estimated using the delta method
(Seber 1982, Alvarez-Buylla and Slatkin 1994),
which included the sampling covariances for the
estimated survival probabilities.
Parameter estimates used to compute l
(Table 2.12) were taken from only the two
population studies because all of the required
parameters were estimated from data within the
same spatial and temporal scales. Survival estimates
were based on the mark-recapture estimators.
Estimates of l were computed separately
for the two studies because of significant differences
in fecundity and juvenile survival between
the two areas.
We obtained estimates of l which were
significantly lower than 1 for the GSA but were
not significantly different from 1 for the CSA
(Table 2.13). These estimates of l represent
trends in populations for only the places and
times of study, and are based on only 3 years of
data collection. We believe the estimate of l
from GSA is 0.288). Presumably,
the best quality territories were incorporated
into the formal monitoring system with a
pair occupancy rate of 67.6% versus 61.0% for

Table Table 2.12.
2.12.
areas.
Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Table 2.12. Parameters used to estimate l for Mexican spotted owls on the GSA a and CSA a study
FPO
Table Table 2.13. 2.13. Estimates and standard errors of l for female Mexican spotted owls on the CSAa and
GSAa study areas. The Z statistic and probability level are for a one-sided test of the null hypothesis of
l < 1 versus the alternative hypothesis l ³ 1.
FPO
20

informal monitoring; and hence, formal monitored
territories were more likely to be occupied.
However, the formal monitoring system looks
more intensively at the sites for owls, so this
difference in occupancy rate may be because of
search procedures, which we suggest as the most
likely scenario.
We examined differences in occupancy rate
(Table 2.15) with a logistic regression model that
included recovery unit, monitoring type (informal
and formal), and the interaction of these
two variables for the years 1989-1993. Type of
monitoring was not significant (c 2 = 0.0191,
1 df, P = 0.890), but recovery unit
(c 2 = 22.7979, 4 df, P < 0.001) and the interaction
of recovery unit and type of monitoring
(c 2 = 16.1657, 4 df, P = 0.003) were significant.
As defined and used here, occupancy rate is
a rather artificial parameter because the selection
of territories for inclusion in the monitoring
database depends on judgement of human
observers. MT boundaries are set subjectively, so
they do not necessarily represent owl home
ranges. Further, MTs may encompass more than
one pair (May et al. in press), although this
possibility is not supposed to occur. Changes in
occupancy rate probably correspond more with
the addition of new MTs to the list of those
already monitored by the FS, level of effort used
Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Table Table 2.14. 2.14. Estimates of population parameters for Mexican spotted owls on the GSAa and CSAa study areas, and the value of the parameter that gives l = 1, provided that all other parameters remain
at their original estimate.
FPO
21
to monitor the MTs (i.e., number of MTs
monitored that meet formal monitoring protocols),
and other administrative factors rather
than true change in the owl population. As a
complicating factor, MTs are not a random
sample of all existing Mexican spotted owl
territories. As can be inferred from Figure 2.2,
the percent of MTs occupied has dropped since
1989 because all new MTs added to the monitoring
system are initially occupied. Habitat
changes induced by forest alterations over the
next several decades will make some of the
currently occupied MTs unsuitable. Thus, we
expect that occupancy rate will decline for
existing territories. New MTs will probably be
added to compensate for loss of existing territories,
so change in occupancy rate does not
provide a valid inference about changes in the
owl population.
Conclusions
Conclusions
We have little confidence in our estimates
of population trends for the following reasons.
First, accurate and precise estimates of l depend
on the accuracy and precision of the parameter
estimates used in the calculations. Estimates of
juvenile survival may be biased low for reasons
stated previously and the time over which
parameters have been estimated is insufficient.

Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Table Table 2.15. 2.15. Number of Mexican spotted owl territories checked (n) and the percent of them occupied
by a pair of owls for 1989-1993, based on formal and informal monitoring methods.
FPO
Second, the population studies from which
parameter estimates were derived have not been
conducted for a sufficiently long period to
capture temporal variation. If one considers l as
an average rate of change over the study period,
then three years is insufficient to adequately
estimate l from both biological and statistical
perspectives. Third, rates of change estimated
through occupancy provide little information on
how Mexican spotted owl populations are
changing for the reasons stated previously.
However, the analysis does illustrate why rates of
population change using occupancy are inadequate
for estimating trends in Mexican spotted
owl populations. If nothing else, we believe the
analytical procedures and framework that we
have used throughout this section should provide
a template for future research as well as
indicate priorities for future research efforts.
Theoretical Theoretical Problems Problems with with Current Current
Current
Monitoring Monitoring Procedures
Procedures
Much effort has been expended by personnel
of FS Region 3 in collecting the monitoring
data summarized here. Unfortunately, the
monitoring effort was inadequate for detecting
important changes in the population dynamics
of the Mexican spotted owl because the appropriate
parameters were not measured.
The primary goal of the monitoring program
should be the detection of significant
changes in population levels of the owl. Such
22
changes can be caused by change in survival rates
or change in reproduction, or both. The current
monitoring program only examines reproduction.
Occupancy rate and pair persistence are
logically flawed approximations to survival.
Thus, with the current monitoring system,
drastic changes in the owl population could
occur and not be detected; or if detected, the
current monitoring system would not yield the
statistical rigor necessary to substantiate the
conclusion strongly enough to withstand the
criticism of opponents to the suggested finding.
Therefore, an improved monitoring system must
be developed for future work (USDI 1995).

Volume II/Chapter 2
Mexican Spotted Owl Recovery Plan
Figure Figure 2.2. 2.2. Changes in occupancy of formal and informal monitoring territories in the FS Region 3
monitoring database.
FPO
FPO
23

Volume II/Chapter 2
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Foster, C. C., E. D. Forsman, E. C. Meslow, G.
S. Miller, J. A. Reid, F. F. Wagner, A. B. Carey,
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Wildlife 2001: populations. Elsevier Applied
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Ganey, J. L. 1988. Distribution and habitat
ecology of Mexican Spotted Owls in Arizona.
M.S. Thesis, Northern Arizona Univ., Flagstaff.
229 pp.
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——., and J.L. Dick, Jr. 1995. Habitat relationships
of the Mexican spotted owl. Pages xxx -
xxxx in USDI. Recovery plan for the Mexican
spotted owl. Vol. 2. USDI Fish and Wildl.
Serv., Albuquerque, N.M.
Gutiérrez, R. J., D. R. Olson, and M. E.
Seamans. 1993. Demography of two Mexican
spotted owl Strix occidentalis lucida populations.
Humboldt State University. Arcata,
California. 16pp.
——., ——., and ——. 1994. Demography of
two Mexican spotted owl populations in
Arizona and New Mexico. Rep. submitted to
Humboldt State Univ. Foundation, Arcata,
Calif. 29pp.
Hansen, A. J., and D. L. Urban. 1992. Avian
response to landscape pattern: the role of
species’ life histories. Landscape Ecol. 7:163-
180.
Hosmer, D. W., and S. Lemeshow. 1989. Applied
logistic regression. John Wiley and Sons,
New York, N.Y. 307pp.
Kaplan, E. L., and P. Meier. 1958. Nonparametric
estimation from incomplete observations.
J. Am. Statist. Assoc. 53:457-481.
Keitt, T., A.B. Franklin, and D.L. Urban. 1995.
Landscape analysis and metapopulation
structure. Chapter 3 (16pp.) in USDI. Recovery
plan for the Mexican spotted owl. Vol. II.
USDI Fish and Wildl. Serv., Albuquerque,
N.M.
Kroel, K. and P. J. Zwank. 1991. Home range
and habitat use characteristics of the Mexican
spotted owl in the southern Sacramento
Mountains, New Mexico. Unpubl. rep.,
USDA For. Serv., Lincoln National Forest.
New Mexico Coop. Fish and Wildl. Unit.
Lebreton, J. D., K. P. Burnham, J. Clobert, and
D. R. Anderson. 1992. Modeling survival and
testing biological hypotheses using marked
animals: a unified approach with case studies.
Ecol. Monogr. 62:67-118.
Leslie, P. H. 1945. On the use of matrices in
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May, C.A., M.Z. Perry, R.J. Gutiérrez, M.E.
Seamans, and D.R. Olson. In press. Feasibility
of a random quadrat study design to estimate
changes in density of Mexican spotted owls.
U.S. For. Serv. Res. Pap.

Moen, C. A., A. B. Franklin, and R. J. Gutiérrez.
1991. Age determination of subadult northern
spotted owls in northwest California.
Wildl. Soc. Bull. 19:489-493.
Noon, B. R., and K. S. McKelvey. 1992. Stability
properties of the spotted owl
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Noon, R. J. Gutiérrez, G. I. Gould, Jr., and T.
W. Beck, eds. The California spotted owl: a
technical assessment of its current status.
USDA For. Serv. Gen. Tech. Rep. PSW-133.
——., and J. R. Sauer. 1992. Population models
for passerine birds: structure, parameterization,
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Paton, P. W. C., C. J. Zabel, D. L. Neal, G. N.
Steger, N. G. Tilghman, and B. R. Noon.
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E. Hines. 1990. Statistical inference for
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——., Winterstein, C. M. Bunck, and P. D.
Curtis. 1989. Survival analysis in telemetry
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Howe, F. Clemente, and J.F. Martinez-
Montoya. 1995. Recovery units. Pages 36-51
in USDI. Recovery plan for the Mexican
spotted owl. Vol. I. USDI Fish and Wildl.
Serv., Albuquerque, N.M.
Roff, D. A. 1992. The evolution of life histories:
theory and analysis. Chapman and Hall. New
York, N.Y. 535pp.
SAS Institute, Inc. 1985. SAS language guide for
personal computers, Version 6. SAS Institute,
Cary, N.C. 429pp.
Seber, G. A. F. 1982. Estimation of animal
abundance. Second ed. C. Griffin, London,
U.K. 654pp.
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Skaggs, R. W., and R. J. Raitt. 1988. A spotted
owl inventory of the Lincoln National Forest,
Sacramento Division, 1988. New Mexico
Dep. Game and Fish, Santa Fe. 12pp.
Stearns, S. C. 1992. The evolution of life histories.
Oxford Univ. Press, Oxford, U.K. 249pp.
Thomas, J. W., E. D. Forsman, J. B. Lint, E. C.
Meslow, B. R. Noon, and J. Verner. 1990. A
conservation strategy for the spotted owl. U.S.
Gov. Print. Off., Washington, D.C. 427pp.
USDA Forest Service. 1990. Management
guidelines and inventory and monitoring
protocols for the Mexican spotted owl in the
Southwestern Region. Federal Register
55:27278-27287.
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Plan. Vol. 1. USDI Fish and Wildl. Serv.,
Albuquerque, N.M.
Usher, M. B. 1972. Developments in the Leslie
matrix model. Pages 29-60 in J. N. R. Jeffers,
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Blackwell Scientific Publ., Oxford, U.K.
Ward, J.P., Jr., S.E. Rinkevich, A.B. Franklin,
and F. Clemente. 1995. Distribution and
abundance. Chapter 1 (14pp.) in USDI.
Recovery plan for the Mexican spotted owl.
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Albuquerque, N.M.
White, G. C., and R. A. Garrott. 1990. Analysis
of wildlife radio-tracking data. Academic
Press, San Diego, Calif. 383pp.
Willey, D. W. 1992a. Semi-annual report: home
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in the canyonlands geographic province;
winter 1991-1992. Unpubl. rep., Utah Div.
Wildl. Resour., Salt Lake City.
——. 1992b. Movements and habitat ecology of
Mexican Spotted Owls in southern Utah.
Final Rep. submitted to Utah Div. Wildl.
Resour., Salt Lake City.
——. 1993. Home-range characteristics and
juvenile dispersal ecology of Mexican spotted
Owls in southern Utah. Unpubl. rep., Utah
Div. Wildl. Resour., Salt Lake City.

Unlike the northern spotted owl (see
Thomas et al. 1990), the range-wide population
of the Mexican spotted owl is naturally fragmented
into geographically distinct subpopulations.
Thus far, we have discussed populations at
the local scale within Recovery Units where
individuals within subpopulations interact to
some degree. Understanding population structure
at larger scales is important, even though
data are extremely limited at these scales for the
Mexican spotted owl. Hanski and Gilpin (1991)
identified two additional scales beyond the local
scale: (1) a metapopulation scale where individuals
infrequently move between subpopulations
and typically cross unsuitable habitat to reach an
adjacent subpopulation, and (2) a geographical
scale where individuals have little likelihood of
moving to most portions of the geographic range
of their species. By definition, metapopulations
are systems of local populations connected by
dispersing individuals (Hanski and Gilpin
1991). The metapopulation concept has been
applied to the conservation of northern
(Schaeffer 1985) and California (Noon and
McKelvey 1992) spotted owl populations.
However, on a geographical scale, the rangewide
population of Mexican spotted owls may be
composed of a several discrete metapopulations
rather than of a single integrated
metapopulation. Understanding to what degree
Mexican spotted owl populations follow
metapopulation dynamics is essential for managing
the subspecies on all three scales.
METAPOPULATION METAPOPULATION MODELS
MODELS
Theoretical work has proposed several
models of metapopulations based on different
mechanisms for persistence. These have been
classified as the Levins model, source-sink, coresatellite,
patchy, and non-equilibrium
metapopulations (Harrison 1991). An important
consideration when reviewing these models is
that empirical evidence for the existence of the
Volume II/Chapter 3
CHAPTER CHAPTER 3: 3: Landscape Landscape Analysis
Analysis
and and and Metapopulation Metapopulation Structure
Structure
Tim Keitt, Alan Franklin, and Dean Urban
1
Mexican Spotted Owl Recovery Plan
proposed mechanisms in natural populations is
debatable (Doak and Mills 1994).
The The Levins Levins Metapopulation Metapopulation Model
Model
Levins (1969) first introduced the
metapopulation concept with a simple model.
This model incorporated three essential requirements
for persistence of a subdivided population:
(1) density-dependent dynamics of populations,
(2) asynchronous dynamics of local
subpopulations in that not all subpopulations
have the same rate of change at the same time,
and (3) dispersal between subpopulations.
Dispersal is an essential component of this, and
all other, metapopulation models and provides
the mechanism for recolonizing areas where local
subpopulations have died out.
Source-sink Source-sink and and Core-satellite
Core-satellite
Metapopulation Metapopulation Metapopulation Models Models
Models
In source-sink models (Pulliam 1988),
source areas with self-propagating (typically
increasing) populations provide a flow of recruits
to sink areas where populations are not selfreproducing
(and may be declining). Without
the net flow of immigrants from the source
areas, populations in sinks would not persist.
Source-sink mechanisms can be applied to
contiguously distributed populations where
habitat conditions can dictate whether a population
segment is a source or a sink. This mechanism
can also be applied to a metapopulation of
discrete subpopulations where habitat or other
conditions dictate whether such an area is a
source or a sink.
The core-satellite model builds on the
source-sink model by having a central core
population which acts as a source surrounded by
a number of smaller sink populations (Harrison
1991). Persistence of the satellite populations
depends upon the central source population.

Patchy Patchy Metapopulation Metapopulation Models
Models
Patchy populations in the context of this
model are characterized by a high dispersal
potential where dispersal takes place on a spatial
scale greater than the local events causing subpopulation
dynamics (Harrison 1991). The
patchy metapopulation model is distinguished
from the Levins model in that the average
individual can belong to more than one subpopulation
in its lifetime (excluding its natal
subpopulation). The result, in effect, is a wellmixed
version of the Levins model.
Non-equilibrium Non-equilibrium Metapopulation
Metapopulation
Model
Model
Populations characterized by this model
essentially follow the same dynamics as the
Levins model except that continuous
recolonization of extinction-prone subpopulations
has been disrupted. Essentially, this model
represents metapopulations in decline even
though one or more subpopulations may be
stable. Instability of a formerly stable
metapopulation may result from factors that
affect one or more subpopulations or when
contiguous populations are fragmented into
discrete subpopulations. These factors can
include natural (e.g., fire, disease) or anthropogenic
(e.g., logging, urban development) disturbances.
Volume II/Chapter 3
DISPERSAL
DISPERSAL
In all metapopulation models, dispersal is a
key component. Dispersal acts as a bridge
between subpopulations at the metapopulation
scale to provide immigrants to otherwise isolated
habitat patches. The fate of these recruits depends
on the status of the subpopulation. If the
habitat patch has been unoccupied, then the new
recruits “rescue” it from extinction. If the patch
is not saturated with territorial breeders, the
recruits might bolster the breeding population.
If the patch is saturated, the new recruits might
persist as nonbreeding “floaters,” perhaps buffering
the population against future fluctuations.
2
Mexican Spotted Owl Recovery Plan
Adult and subadult Mexican spotted owls
appear to be relatively sedentary once they
come to occupy a given site. Juvenile Mexican
spotted owls, however, almost always disperse
from their natal sites (Willey 1993, Hodgson
and Stacey 1994, Reynolds and Johnson 1994).
If metapopulation dynamics apply to Mexican
spotted owl populations, these dynamics probably
hinge on the flow of juvenile spotted owls
between subpopulations.
Dispersal of young Mexican spotted owls is
poorly understood. Several studies have attempted
to examine juvenile dispersal through
radio-telemetry (Willey 1993, Hodgson and
Stacey 1994, Reynolds and Johnson 1994); but
sample sizes have been small. Total distances
moved by 7 juveniles radio-marked in Utah
(Willey 1993) ranged from 32 to 98 km (20-61
miles) (median = 41.8 km [26 miles]). Four of
these juveniles moved back to within 8 km
(5 miles) of their natal area just prior to the
breeding season. Hodgson and Stacey (1994)
also reported 2 juveniles dispersing between the
San Mateo and Black Mountain Ranges of New
Mexico, distances of 45 and 58 km (28-36
miles). In addition, dispersing juveniles crossed
large expanses of habitat typically considered
unsuitable for resident spotted owls. Reynolds
and Johnson (1994) radio-marked 6 juveniles,
none of which were relocated beyond their natal
site. The radio-telemetry data suggest that
juvenile owls have the dispersal capability to act
as recolonizers between many of the subpopulations
and to provide genetic links between
subpopulations. Thus far, none of the radiomarked
juveniles have been recruited into a
resident, territorial subpopulation.
With source-sink and core-satellite
metapopulation mechanisms, juvenile owls from
source areas must not only reach isolated subpopulations
but do so in sufficient numbers to
stabilize sink populations. We examined straightline
distances moved by 25 juveniles banded
from 1991 through 1993 on the population
study areas (CSA and GSA) which had been
recaptured as territorial subadults and adults
(R.J. Gutiérrez, D. Olsen, and M. Seamans,
Humboldt State Univ., Arcata, CA, pers.
comm.). From these data, we generated a probability
function by fitting an exponential curve

to distances moved and the cumulative probability
that juveniles had moved at least those
distance (Figure 3.1). This curve represents the
probability that a juvenile will disperse at least a
given distance and be recruited into the territorial
population. This curve can also be viewed in
terms of proportions. For example, about 60%
of the juveniles would be expected to disperse at
least 10 km (6.2 miles) and be recruited into the
population. We provide this information as an
illustration of the type of data needed to assess
the role of dispersal in metapopulation dynamics.
The data we used were not designed to
generate such a curve and may be artificially
truncated because of lower search effort for
banded recruits in the larger areas surrounding
each of the study areas. Such an effect can be
responsible for the exponential nature of the
relationship in Figure 3.1 and underestimate true
dispersal distances.
APPLICATION APPLICATION OF OF LANDSCAPE
LANDSCAPE
LANDSCAPE
ECOLOGY
ECOLOGY
Landscape ecology is concerned with the
development, implications, and dynamics of
landscape pattern. We use the term “pattern”
generously, but here we are concerned especially
with three components of pattern: (1) the size
distribution of habitat patches; (2) the spatial
orientation of these patches with respect to each
other, that is, their juxtaposition; and (3) their
mutual distance relationships as these might
influence spotted owl dispersal.
With respect to metapopulation dynamics,
landscape analysis is concerned with distance
relationships among habitat patches as these
might affect the relative isolation of certain
patches or regions of patches within the owl’s
range where patches may correspond to distinct
subpopulations. The issue of so-called patch
“connectedness” is central to current ideas about
metapopulation dynamics. By conventional
definition, two patches are functionally connected
if individuals can disperse between them
with a probability or frequency above some
minimum threshold value. We will further
define connectedness to incorporate patch area
as well as between-patch distance relationships
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(see below); thus, a patch may be highly connected
if it is near several small patches or near
one large patch. Specifically, we have two concerns
about patch connectedness:
1. Can we identify habitat patches that
because of their area and position within
the landscape might play a particularly
important role in overall landscape
connectedness? We expect large habitat
patches to be important in this analysis.
2. Are there habitat patches that might be
critical to landscape connectedness
chiefly because of their spatial position,
that is, despite their smaller size? These
might function as dispersal conduits or
small “stepping stones” within the
landscape.
The goal of this set of questions is to identify
habitat patches that might influence patterns in
owl distribution well beyond their immediate
location. In the case of a small stepping-stone
patch, this importance might be despite its
having rather modest owl populations. Thus,
critical patches identified in the landscape
analysis might warrant special consideration in
the Recovery Plan even though their local
populations might not elicit any special concern.
Scale Scale and and Resolution Resolution in in Landscape Landscape
Landscape
Analysis
Analysis
Landscape analysis typically connotes rather
large spatial scales. In our analyses, we have
identified two spatial scales of interest. At a
smaller scale we are concerned with areas such as
a single National Forest, a scale defined in large
part by administrative criteria. At a larger scale
we are concerned with the geographic range of
the owl as we defined it in this plan. We will
refer to these scales as “forest” and “rangewide.”
Importantly, habitat data available at these two
scales is of very different resolution. Data at the
forest scale are of higher spatial resolution
(smaller grain size) and often of higher information
content as well, while data at the rangewide
scale is coarser-resolution and makes fewer

Figur igur igure igur e 3.1 3.1 Dispersal-distance relationship for radio-marked juvenile spotted owls.
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distinctions about habitat details. For example,
many forests have digital elevation models
(DEMs) with a nominal resolution of 30 m (98
ft) and habitat data corresponding to timbermanagement
compartments resolved on the
order of tens of hectares. At this scale, habitats
may be defined in terms of tree-species composition,
size-class distributions, or other details. By
contrast, the data we have available for
rangewide analyses have a spatial resolution of 1
km (0.62 miles); habitats at this scale are defined
as gross cover types (e.g., pinyon-juniper). Data
at these two scales lend themselves to the same
analytic techniques but require rather different
interpretation because of their different resolution
and information content.
Data Data Availability
Availability
In keeping with the foregoing discussion of
scale and resolution, we have attempted to
acquire data at two scales and resolution for
landscape analyses. At a finer scale, we sought
USGS DEMs with 30-m (98 ft) resolution and
4
Mexican Spotted Owl Recovery Plan
habitat maps of similar spatial resolution and
comparatively high information content (e.g.,
species composition, size-class distributions). We
were largely unsuccessful in this effort and, thus,
have been unable to address questions on spatial
aspects of habitat use by owls at this scale.
At a coarser scale, we acquired two sets of
habitat data. Both sets were derived from
AVHRR satellite imagery and have a spatial
resolution of 1 km 2 (0.39 miles 2 ). One set is the
EROS Land Cover classification (Loveland et al.
1991), which recognizes 159 cover classes across
the conterminous United States. The second
dataset is derived from the EROS set but was
reclassified by the FS into a smaller number of
recognized Forest Cover Types (Powell et al.
1993, Zhu and Evans 1992, Evans and Zhu
1993). This latter set also includes a companion
coverage of forest density (percent canopy cover)
derived by resampling the AVHRR-based data
with higher-resolution Thematic Mapper (TM)
imagery at 30-m (98 ft) resolution and correlating
the percent of cells forested at 30-m (98 ft)
resolution to a greenness index (NDVI) at 1-km

esolution (Zhu 1994). The FS has also created a
preliminary classification of Mexico’s forest cover
types, based on the same AVHRR imagery
(Evans et al. 1992). No forest density coverage
exists for Mexico at this time. Examination of
these coverages revealed that the EROS classification
included too much detail and some
details that were rather suspect from a biogeographic
standpoint, both of which argued
against its use. The FS coverages span the entire
range of the owl within the United States and at
an appropriate information content (number of
classes). For these reasons, we have elected to
base our rangewide analyses on the FS coverages.
At this scale, we also have 1-km 2 (0.39 miles 2 )
resolution DEMs as provided by EROS. Because
we lack comparable data for Mexico, our analyses
are restricted to the United States.
The lack of data at higher resolution (e.g.,
30-m scale) has important implications in our
analyses, in that it precludes analysis of those
features too fine-grained to be resolved in the
coarse-resolution data we have been forced to
use. For example, the 1-km scale data cannot
resolve small canyons that are important to owls
in parts of Utah. Neither do we have data that
can resolve details about owl microhabitat, nor
even subtle distinctions among forest cover
types. As we note below, this lack of data does
not render our analyses pointless, but it does
emphasize the need to repeat and corroborate
these analyses with finer-resolution data. On the
other hand, our coarse-resolution approach
allows us to analyze landscape pattern over
virtually all of the owl’s range within the United
States.
Landscape Landscape Connectedness
Connectedness
Connectedness
Our approach derives from graph theory and
percolation theory (Gardner et al. 1992) and
focuses on the so-called “radius of gyration” of
the largest subgraph in a graph representing a
landscape of habitat patches. In this, a “graph” is
a set (map) of habitat clusters, and each “cluster”
is a collection of grid cells that are defined to be
functionally connected. In practice, we define
this connection based on a “minimum joining
distance” such that cells that are within this
distance are functionally connected. The radius
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of gyration is defined as the mean Euclidean
distance between each cell of a habitat cluster
and the centroid of that cluster. Habitat clusters
are formed by specifying a joining distance and
then identifying groups of cells that are spatially
discrete at that distance scale. As one increases
this joining distance, the habitat map coalesces
into increasingly larger clusters as isolated
patches are subsumed into nearby clusters. A
convenient means of indexing this process is as
the radius of the largest cluster in the graph. A
weighted index for the map can be computed by
summing the radii of all clusters in the map,
weighting each radius by the proportion of the
entire map it comprises (i.e., its relative size).
This weighted sum is the map’s “correlation
length” (or connectedness length) and has as
units the distance units of the original map. One
interprets correlation length in terms of how far,
on average, an animal could traverse the map
without straying off “habitat” cells into
nonhabitat.
The ultimate goal here is not to compute
landscape connectedness in itself, but rather to
identify those patches (clusters) that contribute
most significantly to overall habitat connectedness.
One means to this end is to estimate the
reduction in connectedness that would result if a
patch were removed from the landscape. Here,
this estimate is computed as the reduction in
correlation length of the landscape. These
reductions are estimated by systematically
removing each cluster and recomputing the
connectedness index. The analysis itself proceeds
in steps as follows:
1. Define a binary raster map of “habitat”
versus “nonhabitat.”
2. Specify a distance threshold at which
patches may join.
3. Perform the cluster-removal experiment,
saving each cluster’s effect on the correlation
length.
4. Normalize this effect for each cluster by
dividing its effect by its total area, and
save this value as well.

The normalization in step (4) adjusts the
patch’s effect for its area, which identifies those
patches whose effect on connectedness is large
relative to their size. The result of the analysis is
a ranking of habitat patches in terms of the
reduction in connectedness each elicits, that is,
each patch’s contribution to overall connectedness.
This procedure is then repeated for a range
of threshold distances to estimate the consequences
of varying assumptions about the
dispersal capabilities of owls. We used distances
from 0 to 100 km (0-62 miles) in 5-km (3.1
mile) intervals. This range spans our best empirical
estimate of the owl’s dispersal range, which is
on the order of 50 km (31 miles). If the patch
ranks change considerably at different joining
distances, this would suggest a need to improve
the accuracy of our estimates of owl dispersal
distances so that we could tailor the analysis to
maximize its biological significance.
Finally, the entire analysis is repeated for a
variety of baseline habitat maps. This gives us an
estimate of how robust the results are to assumptions
about what constitutes “potential owl
habitat.” At this spatial scale and with the data
available, we have limited opportunities to devise
alternative definitions of “owl habitat.” We have
devised three alternative habitat maps:
1. A map wherein all cells assigned as
“Douglas-fir” (i.e., mixed conifer) or
ponderosa pine (including some mixedconifer
as well as pine-oak) cover types
are defined to be potential owl habitat;
2. A map including all Douglas-fir and
ponderosa pine cells, plus any pinyonjuniper
cells that have greater than 50%
canopy cover as estimated in the FS
Forest Density coverage;
3. A map including all Douglas-fir and
ponderosa pine types, plus those pinyonjuniper
cells that are within a 2-km (1.2
miles) buffer of Douglas-fir or pine
types, i.e., pinyon-juniper near better
owl habitat.
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These alternative definitions vary in terms of
how narrowly or generously “habitat” is defined.
Other definitions could certainly be devised, and
we do not argue that ours are the only (nor even
the best) possibilities. We will argue, however,
that these are sufficient to indicate whether our
conclusions are robust to the definition of
habitat or whether we need to invest more effort
in generating more realistic base habitat maps.
Results Results of of Landscape Landscape Analyses
Analyses
Results of these analyses provide insight into
two keys aspects of habitat connectedness: (1)
the relationship between minimum joining
distance and overall connectedness as indexed by
correlation length; and (2) contributions of
individual habitat patches to overall connectedness.
We present each of these in turn. Because
the results were qualitatively similar for each of
the baseline habitat maps, we present here only
the results for the mixed-conifer/ponderosa pine
base map; but we return to this issue later in our
discussion.
Landscape Landscape Connectedness Connectedness and and and Minimum
Minimum
Joining Joining Distance
Distance
Correlation length exhibits a profoundly
nonlinear relationship with minimum joining
distance in all cases we examined (Figure 3.2).
The inflection in this relationship illustrates that
the landscape changes from being largely “unconnected”
to largely “connected” over a narrow
range of distances. In the habitat maps we
analyzed, this transition occurred over distances
of 40-60 km (25-37 miles). This result varied
only slightly for alternative habitat maps, suggesting
that this qualitative result is rather robust
to these definitions.
The relationship between cluster size and
joining distance varies systematically with the
spatial resolution with which habitats are defined.
This can be seen most clearly by contrasting
the curve for “all clusters” of ponderosa pine
and Douglas-fir as compared to the curve for the
largest 254 of these clusters (Figure 3.2). Including
more (smaller) clusters shifts the curve to the
left, effectively joining the landscape at closer

distances. Presumably, if we were to include very
small clusters the landscape might be functionally
connected at extremely small joining distances,
which is something of a scaling artifact.
This result does underscore the need to more
fully characterize the habitat affinities and
dispersal behavior of owls. If we could limit
cluster sizes and joining (dispersal) distances to
biologically reasonable values, this analysis
would be more confidently focused.
All habitat maps coalesced into a very few
large clusters at joining distances of approximately
60 km (37 miles) or more. This indicates
that at these distances, the entire landscape is
essentially connected (Figure 3.3). Yet even at
joining distances of 100 km (62 miles), a few
clusters remain spatially discrete, and by implication,
functionally isolated from the rest of the
habitat in the landscape.
Rank Rank Rank Patch Patch Contributions Contributions to to Connectedness
Connectedness
Connectedness
The influence of each patch on overall
connectedness was tallied for only the largest
254 clusters in each map. In fact, the maps
contained thousands of clusters but many were
single cells; so it proved to be computationally
impractical to compute every case. Patch influence
on correlation length was strongly dependent
on joining distance: the average influence
was greatest at intermediate distance scales and
much less at shorter or longer scales (Figure 3.4).
To highlight influential patches spatially, we
produced a habitat map in which each patch is
color-coded according to its mean rank over all
distance classes (Figure 3.5a). A similar map
emphasizes patch importance to connectedness
at the intermediate distance scale of 45 km (28
miles) (Figure 3.5b). In both maps, “hot” colors
indicate highly ranked patches (those contributing
substantially to landscape connectedness)
while “cool” colors indicate patches of low rank
(those with little effect on connectedness).
In general, patch effects on connectedness
depended on patch area, in that large patches
had the greatest influence on overall connectedness.
Patch ranks, normalized for area, are
illustrated as averaged over all distances (fig.
3.6a) and at 45-km (28-mile) joining distance
(Figure 3.6b), using the same color scheme as in
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Mexican Spotted Owl Recovery Plan
Figure 3.5. These figures emphasize the importance
of a few clusters in joining the large habitat
block along the Mogollon Rim to the large
cluster farther northeast.
DISCUSSION
DISCUSSION
Distance Distance Relationships Relationships in in in Landscape
Landscape
Connectedness
Connectedness
The nonlinear relationship in Figure 3.2
makes intuitive sense if one envisions the process
that generates this relationship. At small joining
distances, small and nearby patches are joined
into somewhat larger clusters, but the landscape
still consists mostly of disjoint clusters. At a
particular distance, a large subset of the clusters
joins into a single large cluster. Once this has
happened, further small accretions to the cluster
do not change its total area appreciably. From a
functional standpoint, these later additions are
redundant links to an “already connected”
cluster. This same process explains why the
graph of average influence of patch removal
(Figure 3.4) shows a peak at these intermediate
distance classes; for shorter or longer distances
these patches can have little impact on overall
connectedness.
An important result of this analysis is that
the strongly nonlinear domain of this relationship
(i.e., the inflection point in Figure 3.2)
coincides with our best current estimate of the
dispersal capabilities of spotted owls based on
field studies, approximately 50 km (31 miles).
By implication, if owls’ dispersal ranges were
much less than this estimate (say, 20 km [12
miles]) then much of their natural range would
be functionally unconnected (most patches
would be isolated). Reciprocally, if owls could
disperse much farther than our current estimate
(say, 100 km [62 miles]), then most of the
landscape would be functionally connected.
Likewise, the change in this relationship with the
inclusion of more, smaller patches suggests that
owls’ use of very small patches as dispersal
conduits or stepping stones could influence these
results. If owls can use very small patches, then
the landscape might be more connected than our

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Figure Figure 3.2. 3.2. The relationship between correlation length and minimum joining distance. The 4 lines
illustrate the efects of alternative definitions of “potential owl habitat.”
FPO
results suggest, presuming, of course, that such
small patches exist.
The radio-telemetry data suggest that juvenile
owls have the dispersal capability to provide
population and genetic links between subpopulations.
To date, none of the radio-marked
juveniles has been recruited into a resident,
territorial subpopulation. In attempting to judge
whether owl dispersal is sufficient to maintain
population and genetic connectedness, we are
faced with the logistical problem that ecologically
significant dispersal events might occur
quite infrequently (1-2 per generation) and
would likely go unrecorded by even the most
intensive monitoring program. Thus, our data
can suggest that such dispersal capabilities might
exist, but these data cannot prove that such
dispersal actually occurs. Importantly, neither
can our lack of data prove that such dispersal
does not occur.
Clearly these results point to a need for
better understanding of the dispersal behavior
and distance relationships for spotted owls. One
source of uncertainty in our analyses is that the
8
clustering is based on boolean distance decisions
(i.e., patches are connected if their distance is
strictly within the joining distance). But animal
dispersal is probabilistic, exhibiting some sort of
decreasing probability with increasing distance
(recall Figure 3.1). This distinction exaggerates
our results relative to how dispersal probably
occurs with real animals.
A second source of uncertainty stems from
our limited understanding of owl dispersal
behavior. Our analyses are based on assumptions
about “reachability” with the tacit assumption
being that if habitat is reachable in terms of
absolute distance, then owls can and will disperse
there. But there are many plausible reasons why
this might not be so (e.g., avoidance behavior,
excessive mortality during dispersal); so it
remains that we need to temper our interpretations
with additional considerations of owl
dispersal.

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Figure Figure 3.3. 3.3. Landscape mosaics of discrete clusters of Douglas-fir and Ponderosa pine habitat types, as
(a) (a) largest 254 clusters, and at (b) (b) 30-km, and (c) (c) 60-km joining distances. Colors have no significance
beyond labelling discrete clusters.
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Figure Figure 3.4. 3.4. Change in correlation length due to cluster removal as a function of distance, averaged
over the largest 254 clusters.
FPO
Patch Patch Contributions Contributions to to Landscape
Landscape
Connectedness
Connectedness
Rank scores for patch contributions to
overall landscape connectedness make intuitive
sense when viewed as landscape mosaics (Figures
3.5 and 3.6). The ranks uncorrected for area
show the expected result that large clusters that
are centrally located have the highest ranks,
while small or isolated clusters are lower-ranked.
Area-normalized ranks emphasize the positional
aspects of patch contributions and Figure 3.6
illustrates a few patches (in red) that seem to act
as bridges spanning larger habitat areas. Some of
these bridges are rather small yet could be
important links in landscape connectedness.
An important caveat to bear in mind is that
these analyses are all based on habitat, not on
owl densities. Thus, sparsely populated habitat
clusters in the northern reaches of the owl’s
range receive equal weight in the analysis as
compared to habitats currently supporting much
larger owl populations, for example, along the
10
Mogollon Rim. Thus, the clusters in Colorado
that appear important to connectedness (red
patches in the upper-right regions of Figure 3.5)
are actually connecting habitat that supports
essentially no owls. If habitat clusters were
weighted according to present-day owl abundance,
these same analyses would provide quite
different results. Densely populated patches
would increase in importance while more
sparsely populated patches would be downweighted.
While this is rather easy to anticipate
in general, such a weighted analysis would
require much better spatial information on owl
abundance across its range than the inconsistent
coverage currently available.
These considerations bear strongly on the
ultimate goal of a conservation plan. If our goal
is to provide a template that might sustain owl
metapopulations well into the future, then an
analysis weighted on “potential habitat” seems
most appropriate. Conversely, a strategy to
preserve current populations would seem to
argue for an analysis heavily weighted on
present-day owl abundance. Our results suggest

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Mexican Spotted Owl Recovery Plan
Figure Figure 3.5. 3.5. Maps with clusters colored to illustrate their rank importance, weighted by (uncorrected
for) patch area. Hot colors (reds) are highly ranked; cool colors (blue-violet), low ranked. Base habitat
map is ponderosa pine/Douglas fir. (a) (a) Patch importance averaged of all distance classes. (b) (b) Importance
at 45-km joining distance.
11

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Mexican Spotted Owl Recovery Plan
Figure Figure 3.6. 3.6. Patch importance to overall connectedness, normalized for patch area. Color scheme and
base map, and panels (a) (a) and (b) (b) (b), (b) are the same as in Figure 3.5.
12

that these two strategies might lead to quite
different recommendations.
Importantly, our rankings of patch importance
to overall connectedness are based on a
simple patch-removal algorithm in which each
patch is removed singly from the existing landscape.
Clearly, these results could be quite
different if the algorithm provided for more
complex scenarios as conditional removals. For
example, if patch i has already been removed,
then the removal of patch j might take on much
greater importance. Such conditional scenarios
would be more realistic in the sense that landscape
dynamics driven by land-use management
are time-structured (sequential), conditional, and
typically act on multiple patches during any
single management episode. Such complicated
scenarios might be undertaken on a smaller scale
(e.g., for a National Forest) if sufficient data were
available for the analysis. Complicated, conditional
scenarios are probably not feasible for
rangewide analyses.
Sensitivity Sensitivity to to Habitat Habitat Definition
Definition
Two empirical biases emerge in considering
alternative definitions of what constitutes “potential
owl habitat” in these analyses. One bias is
due to the spatial scale at which habitat patches
are resolved. As smaller patches are included,
overall landscape connectedness tends to increase
so long as these small patches are liberally
sprinkled across the landscape. Similarly, for
habitat definitions that are increasingly “generous”
toward owls, more potential owl habitat
occurs in the landscape and so connectedness
also tends to increase (consider a map that
includes some pinyon-juniper relative to the
mixed-conifer/pine landscape). These biases
appear in our analyses as a result of data availability.
If higher-resolution data were available,
more patches could possibly be delineated. At
the same time, however, given higher-resolution
data we could define owl habitat more stringently
and thus some patches would be redefined
as no longer usable by owls; owl habitat
would decrease in abundance and overall connectedness
would decrease accordingly. Thus, the
two empirical biases are somewhat compensat-
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ing. But both biases point to a need to improve
our ability to discriminate usable owl habitat
from the surrounding matrix.
Other Other Uncertainties Uncertainties and
and
Considerations
Considerations
A final consideration of our results must
address any uncertainties or biases that might
result from the algorithm itself. One potential
bias that emerges can be seen in the figures
illustrating patch importance to connectedness.
Because our approach indexes connectedness as
the mean size of the largest cluster, a bias
emerges whereby patches that are peripheral in
the landscape can form clusters with a very large
radius. Thus, the important patches in Figure
3.5 tend to form a ring around the landscape as a
whole, partly because these patches are large but
also because their joining creates a cluster that
has a radius nearly as large as the entire mosaic.
This bias would not occur if the index of connectedness
counted total area in a way that did
not emphasize among-cell distances. For example,
an index that estimated “total connected
area” rather than the effective size of this area
might yield a slightly different estimate of patch
importance. Unfortunately, such indices have
proven to be computationally unfeasible thus far.
We continue to explore alternative algorithms
for indexing habitat connectedness.
CONCLUSIONS
CONCLUSIONS
Application of metapopulation theory to the
Mexican spotted owl is rather speculative, given
our limited understanding of within-population
dynamics much less between-population dynamics.
If metapopulation models actually represent
realistic abstractions of real-world processes, then
a number of different metapopulation models
may apply to different geographic regions within
the range of the Mexican spotted owl. For
example, one could envision a core-satellite
model applying to the southern portion of the
Mexican spotted owl range with the Upper Gila
RU acting as a core source population with the
smaller surrounding mountain ranges in Basin

and Range - West and Colorado Plateau RUs
acting as satellite sinks. On the other hand, the
Sky Island mountain ranges in southern Arizona
could also follow the classic metapopulation
dynamics proposed by Levins (1969). A number
of different scenarios could be envisioned,
which, unfortunately, we cannot corroborate
easily empirically. The distribution of geographically
isolated subpopulations, however, suggests
that some form of interaction between these
subpopulations is plausible. Clearly, intensive,
long-term studies over large areas will be required
to understand the structure and dynamics
of Mexican spotted owl population at these large
scales.
Although the landscape analyses are exploratory,
some general conclusions can still be
drawn from the results. These conclusions
concern apparent connectedness of various
regions of the owl’s range and the relative importance
to particular habitat clusters to overall
landscape connectedness.
Regardless of the underlying habitat map
used in analyses, results consistently show a few
regions that appear functionally isolated at
intermediate joining distances similar to the
dispersal range of owls. For example, large blocks
of southern Utah persist as discrete habitat
clusters at joining distances of 40 km (25 miles);
the Lincoln National Forest also appears isolated
at this spatial scale. We might test the hypothesis
that these subpopulations are discrete, possibly
by exploring genetic similarities between these
and more central (connected) populations such
as those along the Mogollon Rim. Likewise,
basic population analyses of these populations
might also indicate their degree of functional
connectedness. For example, spatial
discontinuities in population density, age structure,
or other parameters might suggest that
these populations do not interact to the same
extent as other, more contiguous populations.
The relative importance of individual habitat
patches, when uncorrected for patch area,
suggests the intuitive approach of protecting
those patches that currently support the highest
owl densities, such as along the Mogollon Rim.
But our results also indicate a high importance
for patches farther north in the owl’s range,
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patches which currently do not support appreciable
owl populations. Our reaction to this
result depends in part on whether our goal is to
preserve present-day populations or to protect
the capability for populations to expand in the
future. The discrepancy between these two
strategies is most pronounced in the northern
reaches of the owl’s current range.
Correcting cluster importance for area
indicates the contribution, per unit area, of each
of the habitat clusters. This correction suggests
that while the cluster along the Mogollon Rim is
crucial to overall connectedness, the many stands
making up this cluster are not so important on
an individual basis. Thus, this cluster would
likely continue to play an important role in the
landscape so long as its internal continuity is
maintained, which would require reiterating our
analyses on a finer spatial scale and resolution as
management of this region proceeds. Conversely,
a few clusters emerge as being more important
per unit area than their uncorrected importance
would suggest, such as the stepping-stones
evident in Figure 3.6 as red patches. Such
patches warrant special attention in land use
planning because of their potential to affect
regional populations despite their small size and
perhaps modest owl populations. Especially,
these patches should be a focus of monitoring
efforts so that their use by owls can be assessed.
Note that these patches typically would not be
targeted in field studies for the simple reason
that they would not appear to support large owl
populations.
Finally, we should emphasize that these
results are exploratory and therefore subject to
corroboration. One form of verification could
come via analyses of owl subpopulations across
the region. Metapopulation theory suggests that
isolated habitats should show higher year-to-year
variability in population density than would
better-connected patches, which would be better
subsidized by dispersal. A second form of corroboration
would entail analyses similar to ours
but using alternative indices of connectedness
and alternative definitions of suitable owl habitat.
Especially, we would like to see these analyses
repeated with higher-resolution habitat data
capable of resolving the those features most
important to owls. In any case, it is clear that we

need to invest much more effort toward defining
the dispersal capabilities and behavior of the
spotted owl across its range.
In closing, we would like to revisit the
rationale that underlies our somewhat theoretical,
habitat-based approach. While it might be
appealing to invoke analyses that rely on owl
population data, we were forced to accept at the
beginning that we lacked adequate data for such
an analysis across the owl’s range. Similarly,
detailed population models such as those developed
for the northern owl are appealing because
of their biological richness; but we clearly lack
the data to parameterize such a model for the
Mexican spotted owl. We see both these population-based
approaches as a useful adjunct to our
approach, but one that we cannot support
empirically with data currently available. Instead,
we developed an approach that makes very few
assumptions about owl biology, and we tested
our results to determine whether violation of
these assumptions would change our results
substantially. Our approach was to use as generous
a definition of owl habitat as possible given
our data; our major conclusions seem largely
unaffected by alternative definitions of habitat,
although this needs to be verified with finerresolation
data. The other important assumption
we made was that owls have a dispersal-distance
relationship such that dispersal probability
decreases with increasing distance, and that their
average dispersal is in the neighborhood of 50
km or so (i.e., not > 100
km). Within this domain, our results are also
robust. Thus, while there remain a number of
questions still to be resolved concerning landscape-scale
patterns and owl metapopulations,
the results we present here are a useful and valid
first approximation.
Volume II/Chapter 3
15
Mexican Spotted Owl Recovery Plan
LITERATURE LITERATURE CITED
CITED
Doak, D. F., and L. S. Mills. 1994. A useful role
for theory in conservation. Ecology
75:615-626.
Evans, D. L., and Z. Zhu. 1993. AVHRR for
forest mapping: national applications
and global implications. Pages 76-79 in
A. Lewis, ed. Looking to the future with
an eye on the past: proceedings of the
1993 ACMS/ASPRS. ASPRS.
——., Z. Zhu, S. Eggen-McIntosh, P. G. Mayoral,
and J. L. Omelas de Anda. 1992.
Mapping Mexico’s forest lands with
advanced very high resolution radiometer.
USDA For. Serv. Southern For. Exp.
Stn., New Orleans, La.
Gardner, R. H., M. G. Turner, V. H. Dale, and
R. V. O’Neill. 1992. A percolation
model of ecological flows. Pages 259-269
in A. J. Hansen and F. di Castri, eds.
Landscape boundaries. Springer-Verlag,
New York, N.Y.
Hanski, I., and M. Gilpin. 1991.
Metapopulation dynamics: brief
history and conceptual domain. Biol. J.
Linnean Soc. 42:3-16.
Harrison, S. 1991. Local extinction in a
metapopulation context: an empirical
evaluation. Biol. J. Linnean Soc. 42:73-
88.
Hodgson, A., and P. Stacey. 1994. Habitat use
and dispersal by Mexican spotted owls.
U.S. For. Serv., Rocky Mtn. For. Rng.
Exp. Stn., Flagstaff, Ariz.
Levins, R. 1969. Some demographic and genetic
consequences of environmental heterogeneity
for biological control. Bull.
Entomol. Soc. Amer. 15:237-240.
Loveland, T. R., J. W. Merchant, D. O. Ohlen,
and J. F. Brown. 1991. Development of a
land-cover characteristics database for the
conterminous U.S. Photogrammetric
Eng. and Remote Sensing 57:1453-
1463.
Noon, B. R., and K. S. McKelvey. 1992. Stability
properties of the spotted owl
metapopulation in southern California.
Pages 187-206 in J. Verner, K. S.

McKelvey, B. R. Noon, R. J. Gutiérrez, G. I.
Gould, Jr., and T. W. Beck, eds. The
California spotted owl: a technical
assessment of its current status. USDA
For. Serv. Gen. Tech. Rep. PSW-133,
Pac. Southwest Res. Stat., Albany, Calif.
Powell, D. S., J. L. Faulkner, D. Darr, Z. Zhu,
amd D. W. MacCleery. 1993. Forest
resources of the United States. USDA
For. Serv. Gen Tech Rep. RM-234,
Rocky Mtn. For. Range Exp. Stat., Ft.
Collins, Colo.
Pulliam, H. R. 1988. Sources, sinks, and population
regulation. Am. Nat. 132:652-
661.
Reynolds, R. T., and C. L. Johnson. 1994.
Distribution and ecology of the Mexican
spotted owl in Colorado: annual report.
USDA For. Serv., Rocky Mtn. For. Rng.
Exp. Stn., Ft. Collins, Colo.
Schaffer, M. L. 1985. The metapopulation and
species conservation: the special case of
the northern spotted owl. Pages 86-99 in
Volume II/Chapter 3
16
Mexican Spotted Owl Recovery Plan
R. J. Gutiérrez and A. B. Carey, eds.
Ecology and management of the northern
spotted owl in the Pacific Northwest.
USDA For. Serv. Gen. Tech. Rep. PNW-
185, Portland, Oreg.
Thomas, J. W., E. D. Forsman, J. B. Lint, E. C.
Meslow, B. R. Noon, and J. Verner.
1990. A conservation strategy for the
spotted owl. U.S. Gov. Print. Off.,
Washington, D.C. 427pp.
Willey, D. W. 1993. Home-range characteristics
and juvenile dispersal ecology of Mexican
spotted Owls in southern Utah.
Unpubl. Rep., Utah Div. Wildl. Resour.,
Salt Lake City.
Zhu, Z. 1994. Forest density mapping in the
lower 48 states: a regression procedure.
USDA For. Serv. Res. Pap. SO-280,
Southern For. Exp. Stat., New Orleans,
Louis.
——., and D. L. Evans. 1992. Mapping
midsouth forest distributions with
AVHRR data. J. For. 90:27-30.

Volume II/Chapter 4
CHAPTER CHAPTER 4: 4: Habitat Habitat Relationships Relationships of of the
the
Mexican Mexican Mexican Spotted Spotted Owl: Owl: Current Current Knowledge
Knowledge
The Mexican spotted owl was listed as
threatened primarily due to concerns over loss of
habitat (USDI 1993). Consequently, understanding
the habitat relationships of the Mexican
spotted owl is critical to developing sound
management plans for this species. Here, we
summarize both recent and historical information
on habitat relationships of Mexican spotted
owls. Because most historical information on the
owl’s habitat contains little quantitative information,
we rely mainly on recent information
(1985 - present time).
Our primary objectives in this treatment are
to: (1) evaluate and describe patterns of habitat
use by Mexican spotted owls; (2) evaluate and
describe patterns of habitat selection by Mexican
spotted owls; (3) identify specific habitats or
habitat components that appear to be particularly
important to the owl; and (4) identify areas
where further information on habitat relationships
of this owl are most needed. We use the
terms habitat, habitat use, and habitat selection
as defined by Block and Brennan (1993). Thus,
habitat as used here refers to “the subset of
physical environmental factors that a species
requires for its survival and reproduction” (Block
and Brennan 1993:36). Habitat use refers to “the
manner in which a species uses a collection of
environmental components to meet life requisites”,
and habitat selection refers to “disproportional
use of environmental conditions” (Block
and Brennan 1993:38).
Patterns of habitat use evaluated here are
largely descriptive. We evaluated patterns of
habitat selection by comparing use of vegetation
types or specific habitat components to the
occurrence of those types or components.
Ecological patterns and processes vary with
spatial scale (Urban et al. 1987, O’Neill et al.
1988, Turner 1989), however, and considering
patterns of resource use at only one scale can
yield misleading results (Porter and Church
1987, Orians and Wittenberger 1991, Block and
Brennan 1993). Therefore, we used a number of
data sources, both published and unpublished,
Joseph L. Ganey and James L. Dick, Jr.
1
Mexican Spotted Owl Recovery Plan
to examine habitat use and/or selection at five
spatial scales. At some scales we could evaluate
habitat selection, whereas at others we could
only describe patterns of habitat use. Scales
examined are described below, arrayed from
coarsest to finest scale:
1. Landscape scale - habitat use across the
entire range of the Mexican spotted owl.
2. Home-range scale - patterns of habitat
use within owl home ranges as defined
by locations of radio-tagged owls.
3. Stand scale - use of relatively homogeneous
units of forest vegetation within
owl home ranges.
4. Site scale - habitat use proximate to nest,
roost, and foraging sites.
5. Tree scale - use of individual roost and
nest trees.
In some cases, we reanalyzed existing data
sets to provide more detailed information or to
explore different questions than those asked by
original investigators. Methods varied among
studies, and will be discussed in conjunction
with the specific data examined. Some of the
data used were from ongoing studies, and some
of the analyses are preliminary. Therefore, while
the information presented here represents the
current state of knowledge on habitat relationships
of Mexican spotted owls, we caution that
additional trends may emerge with further data
collection and analysis.

PATTERNS PATTERNS OF OF HABITAT HABITAT USE USE AT
AT
THE THE LANDSCAPE LANDSCAPE SCALE
SCALE
Literature Literature Literature Review
Review
Available historical information on habitat
use by Mexican spotted owls in Arizona and
New Mexico was reviewed in Johnson and
Johnson (1985), Ganey (1988), Ganey et al.
(1988), and Skaggs (1988), and summarized
across the range of the owl in McDonald et al.
(1991). Most reports of Mexican spotted owls in
both popular and technical literature are anecdotal
and contain little detailed information.
These reports were typically results of faunal
surveys that reported areas where they found
species. As such, they were neither systematic
nor complete samples, and are thus biased
towards the few places where spotted owls were
located. While these reports provide some
information on areas where owls were located,
they should not be viewed as the ultimate word
on habitats used by spotted owls.
With these cautions in mind, the general
picture that emerges is that owls occurred in
habitats ranging from low elevation riparian
forests (Bendire 1892, Phillips et al. 1964, and
possibly Woodhouse 1853:63) to high elevation
coniferous forests, but were most common in
high elevation coniferous and mixed coniferousbroadleaved
forests, often in canyons. In perhaps
the most detailed historical account of the
Mexican spotted owl, Ligon (1926:422) described
its typical haunts as “deep, narrow,
timbered canyons where there are always cool
shady places.”
Several recent studies describe habitats used
by Mexican spotted owls. For example, Kertell
(1977), Rinkevich (1991), and Willey (1992)
reported on habitats occupied by Mexican
spotted owls in southern Utah (Colorado Plateau
RU). All reported that owls were typically found
in narrow, steep-walled canyons, and all suggested
that distribution was restricted by the
availability of such canyons. Reynolds (1993)
also reported finding owls only in “steep-walled,
deeply-cut canyons characterized or dominated
by exposed rocky slopes and tiers of rock cliffs”
in Colorado (Colorado Plateau and Southern
Volume II/Chapter 4
2
Mexican Spotted Owl Recovery Plan
Rocky Mountains-Colorado Recovery Units; see
USDI 1995 for discussion of specific Recovery
Units [RUs] within the range of the Mexican
spotted owl).
Ganey and Balda (1989a) recorded cover
type at 55 roost sites in northern Arizona, of
which 53 were located in the Upper Gila Mountains
RU. Of these, 92.4% were located in
mixed-conifer forest. The remaining 7.6% were
classified as ponderosa pine, but more likely were
in ponderosa pine-Gambel oak forest. Most were
located in steep canyons or on montane slopes.
Also in this RU, Seamans and Gutiérrez (in
press) recorded cover type at 79 roost and 28
nest sites in the Tularosa Mountains, New
Mexico. These owls roosted and nested primarily
in mixed-conifer forests containing an oak
component, usually on the lower third of northfacing
slopes (Seamans and Gutiérrez in press:
fig. 1).
In the Basin and Range-West RU, Ganey
and Balda (1989a) recorded cover type at 64
roost sites. Most were in mixed-conifer (48.4%)
or Madrean pine-oak (29.7%) forest, with
14.1% in encinal (evergreen oak), and 7.8% in
ponderosa pine forest. At 19 roost and/or nest
sites observed by Duncan and Taiz (1992) in this
RU, 31.6% were in mixed-conifer forest, 31.6%
in Madrean pine-oak forest, 26.3% in Arizona
cypress forest, and 10.5% in encinal. In both
studies, most owls were observed in montane
canyons.
Skaggs and Raitt (1988) surveyed 42,105 ha
(104,000 acres) in the Basin and Range-East
RU. Survey areas were divided into 18 plots of
23.3-km 2 (9-mi 2 ) prior to survey, with all plots
classified by the dominant forest type within the
plot (6 each in mixed-conifer, ponderosa pine, or
pinyon-juniper). They found 33 occupied sites;
72.7% in mixed-conifer, 18.2% in ponderosa
pine, and 9.1% in pinyon-juniper. Even in plots
classified as ponderosa pine or pinyon-juniper,
the owls typically roosted in pockets of mixedconifer
forest (Roger Skaggs, New Mexico State
Univ., Las Cruces, NM, pers. comm.). Kroel
(1991:39) also noted that owls in this RU
roosted primarily (79% of observed roosts) in
mixed-conifer forest, with limited use of ponderosa
pine forest and pinyon-juniper woodland
(14 and 4% of all roosts, respectively).

Little recent information exists regarding
habitat use by spotted owls in Mexico. However,
Tarango et al. (1994) reported finding Mexican
spotted owls in isolated patches of pine-oak
forest in steep canyons in the Sierra Madre
Occidental-Norte.
With regard to all of the above studies, it is
important to note that definitions of cover types
may have varied slightly among observers, and
we cannot be certain that cover types are completely
consistent with definitions used in this
Plan.
Recovery Recovery Team Team Analysis Analysis of of Recent
Recent
Inventory Inventory Data
Data
Recent inventories by land management
agencies, particularly the U. S. Forest Service
(FS), have generated considerable information
on owl locations and habitats used. We used this
information to evaluate use of vegetation (or
cover) types across the range of the subspecies.
Crews visited FS District and Supervisors offices,
collated inventory and monitoring data from
1990 (when survey efforts were standardized
throughout the Region) to 1993 (when these
data were collated), and entered the information
gathered into a data base. These same crews also
collated records from the NPS, BLM, Tribal
lands, State wildlife agencies, Fort Huachuca
Military Reservation, and independent researchers
in both the United States and Mexico for the
same time period. Thus, we attempted to gather
all existing information on current distribution
and habitat use of the Mexican spotted owl
across its range.
Vegetation type at nest or roost sites was
entered directly from field data forms, with types
generally corresponding to Series level designations
described in Brown et al. (1980). We could
not assess the accuracy or consistency of habitat
classification across the range of the owl. All
locations for which vegetation type information
was missing or ambiguous were omitted from
analysis.
We used only visual observations (such as
birds at roost and nest sites) to assess habitat use
because habitat cannot be determined for distant
owls heard at night. Most roost or nest locations
Volume II/Chapter 4
3
Mexican Spotted Owl Recovery Plan
entered in this database could not be assigned to
a particular “management territory.” As a result,
we are uncertain how many unique pairs of owls
were represented, or how many roost or nest
sites might represent a single pair. This potentially
serious lack of independence in the data
rendered statistical comparisons among RUs or
between roost and nest sites meaningless. Therefore,
we simply present summaries of vegetation
types used for roosting and nesting by Recovery
Unit. We could not compare habitat use with
habitat occurrence at this scale, because of the
problems discussed above regarding lack of
independence, because no geographical information
system (GIS) coverage was available documenting
areas surveyed, and because we were
unable to obtain a rangewide vegetation type
coverage. The closest we could come to a
rangewide vegetation type coverage covered only
the U. S. portion of the range of the Mexican
spotted owl, and had a minimum resolution of 1
km 2 (Keitt et al. 1995). This scale is not appropriate
for evaluating roost and nest sites, which
require a much finer scale of resolution.
Mexican spotted owls used a variety of
vegetation types across their range (Table 4.1).
Although the range of vegetation types used
varied among RUs, mixed-conifer forest was
heavily used in most RUs. In contrast, encinal
was used only in the Basin and Range-West, and
pine-oak forest was used primarily in the Basin
and Range-West and Sierra Madre Occidental-
Norte. The pine-oak forest found in these RUs is
Madrean in affinity and differs in both species
composition and habitat structure from the
ponderosa pine-Gambel oak forest found in
other RUs (Brown et al. 1980, Ganey et al.
1992). Ponderosa pine forest was used rarely, and
pinyon-juniper woodland was used primarily by
owls in the Colorado Plateau. Riparian forest
was used in several RUs, but at relatively low
levels.
We could not statistically compare RUs
because of the problems discussed above. Based
on discussions with researchers and managers
familiar with local situations, however, we
believe that the observed differences in patterns
of habitat use among RUs are both real and
ecologically important.

4
Table Table 4.1. 4.1. Percent of nest (top row) and roost (bottom row) sites in various vegetation types in different Recovery Units. Based on analysis of inventory
and monitoring data collected since 1990. Vegetation types follow Series in Brown et al. (1980).
FPO

PATTERNS PATTERNS OF OF HABITAT HABITAT USE USE AT
AT
THE THE THE HOME-RANGE HOME-RANGE SCALE
SCALE
Home-Range Home-Range Size
Size
Several studies have examined home-range
size and/or habitat use within home ranges of
radio-tagged Mexican spotted owls. Minimum
convex polygon (MCP; Mohr 1947) and 95%
adaptive kernel (AK; Worton 1989, where
possible) estimates of home-range size from these
studies are presented in Table 4.2. Estimates are
presented separately for each study area. Homerange
size appeared to vary considerably among
study areas, even within a restricted geographic
area (Table 4.2). For example, Zwank et al.
(1994) found that home-range size differed
significantly between two drainages in the
Sacramento Mountains, New Mexico. Ranges
were smaller in the Rio Penasco watershed (n = 5
owls), where mixed-conifer forest comprised 65-
86% of home ranges, than in the Sixteen Springs
watershed (n = 4 owls), where mixed-conifer
forest comprised only 6-42% of home ranges,
with most of the remainder consisting of ponderosa
pine forest and pinyon-juniper woodland
(Zwank et al. 1994: table 1). Similarly, Ganey
and Balda (1989b) observed large differences in
home-range size among owls on the San Francisco
Peaks and in Walnut Canyon. Although
these areas are separated by only approximately
16 km (10 mi), habitat composition differs
between the two areas (Ganey and Balda 1994:
table 3). These results suggest that home-range
size of Mexican spotted owls may vary among
cover types. However, small numbers of owls
tracked in all studies, as well as differences in
sampling intervals and seasons covered limit our
ability to make comparisons among study areas.
Consequently, we caution that these numbers
represent general estimates of areas used by
spotted owls, and as such do not support sweeping
generalizations about differences between
areas and/or cover types.
Size Size of of Activity Activity Centers
Centers
Gutiérrez et al. (1992) suggested that the
smallest area encompassing 50% of nocturnal
Volume II/Chapter 4
5
Mexican Spotted Owl Recovery Plan
foraging locations (the 50% adaptive kernel)
could define a foraging activity center. Because
of the great variability in available estimates of
home-range size for Mexican spotted owls, we
took a more conservative approach and defined a
nocturnal activity center based on the area
enclosed by the adaptive kernel contour encompassing
75% of foraging locations. This activity
center was defined only for territories where
both pair members were radio-tagged. In general,
owls appeared to forage primarily within a
relatively small portion of the home range,
suggesting high concentration of activity (Table
4.3). This pattern appeared to hold regardless of
RU or study area (but see above cautions regarding
comparisons among studies).
Habitat Habitat Composition Composition and and Use
Use
Three studies quantified habitat composition
within MCP home ranges of radio-tagged owls
(Willey 1993, Ganey and Balda 1994, Zwank et
al. 1994). Home ranges were most variable in
terms of vegetation types in the Colorado
Plateau RU, encompassing types ranging from
mixed-conifer forest to mountain shrub and
grassland (Willey 1993: table 4). Home ranges
were dominated by mixed-conifer and ponderosa
pine forests in the Upper Gila Mountains RU
(Ganey and Balda 1994), and by mixed-conifer
forest, ponderosa pine forest, and pinyon-juniper
woodland in the Basin and Range-East RU
(Zwank et al. 1994).
Ganey and Balda (1994) compared use of
vegetation types by foraging, radio-tagged owls
to the area of those types within the MCP home
range (a measure of relative availability), using
chi-square tests and Bonferroni confidence
intervals (Neu et al. 1974, Byers et al. 1984).
This comparison involved eight owls representing
five pairs on three study areas.
Observed patterns of habitat use by foraging
owls were complex. In relation to area of different
forest types within their home ranges, all
individual owls used forest types nonrandomly.
All forest types were used by foraging owls. In
general, individual owls foraged significantly
more than or as expected in unlogged forests and
significantly less than or as expected in selec-

6
Table Table 4.2. 4.2. Home-range sizes (ha) of radio-marked Mexican spotted owls. Part A shows ranges of pairs with both members radio-tagged; part B shows
ranges for individual owls. Study areas represent mesic mixed-conifer forest on the San Francisco Peaks (SFP), White Mountains (WM), and Sacramento
Mountains (SM-MC); a mixture of mixed-conifer, ponderosa pine, and xeric pinyon-juniper in the Sacramento Mountains (SM-XE); a rocky canyon
(Walnut Canyon, WC); ponderosa pine-Gambel oak forest near Bar-M Canyon (BMC); rugged canyons with mixed forests in the San Mateo Mountains
(SANMAT); a mixture of mesic mixed-conifer forest and pinyon-juniper in rocky canyons along Elk Ridge (MANTI) and in Zion National Park (ZION);
and xeric pinyon-juniper in rocky canyons in Capitol Reef and Canyonlands National Parks (CNP). Shown are the means (± SD) for 100% minimum
convex polygon (MCP) and 95% adaptive kernel (95% AK) estimates.
FPO

7
Table Table 4.2. 4.2. (continued)
FPO

8
Table Table 4.3. 4.3. Size (mean ± standard deviation) of nocturnal activity centers of radio-tagged pairs of Mexcan spotted owls in the Upper Gila Mountains and
Basin and Range-East Recovery units. Activity centers defined as the area included in the adaptive kernel contour enclosing 75% of owl foraging locations.
FPO

tively logged forest types (Table 4.4). This
comparison is overly simplistic, however. Both
logged and unlogged forests contained a wide
range of stand structures. Some logged stands
were used for foraging, and some unlogged
stands were not used. In addition, two of the
unlogged forest types (virgin mixed-conifer
forest on rocky slopes and ponderosa pine-oakjuniper
forest) were found primarily on rocky
slopes interspersed with significant rock outcrops
and cliffs, and owls appeared to forage in these
rocky areas as well as in the forest (Ganey and
Balda (1994:165). Thus, these findings do not
indicate that all unlogged stands provide suitable
foraging conditions and that all logged stands do
not. Rather, they suggest that patterns of habitat
use by foraging owls are complex and not amenable
to simplistic explanations. At this time, we
cannot explain why some logged forests are used
and others are not.
Differences in patterns of habitat use among
and within study areas also suggest that patterns
of habitat use for foraging are complex. Use of
particular forest types sometimes varied considerably
among individual owls within a study area
(Table 4.4), and even between members of a
mated pair (Ganey and Balda 1994: table 3). In
short, there is considerable variability in patterns
of habitat use for foraging. As a result, it is
difficult to generalize about patterns of habitat
selection by foraging owls based on currentlyavailable
data.
In contrast to the variable patterns observed
among foraging owls, patterns of habitat use by
roosting owls were relatively consistent among
study areas and individual owls. Habitat use for
roosting was not compared statistically to habitat
occurrence because of small sample sizes for
some individual owls. All owls roosted primarily
in unlogged mixed-conifer forests, but some
used unlogged ponderosa pine forest as well
(Ganey and Balda 1994; table 3). Very little
roosting occurred in logged stands, particularly
during the breeding season.
Volume II/Chapter 4
9
Seasonal Seasonal Movements Movements
Movements
Mexican Spotted Owl Recovery Plan
Most Mexican spotted owls appear to remain
in the same general area throughout the year,
whereas others migrate in winter, usually to
lower elevations. Year-round residents often use
larger ranges during the nonbreeding season
than during the breeding season (Kroel 1991,
Willey 1993, Ganey and Block unpublished
data), and there appear to be shifts in use of area
and habitat for some owls (Ganey and Balda
1989b, Kroel 1991, Willey 1993, Ganey and
Block unpublished data). No quantitative results
are yet available that describe wintering habitats
used by owls remaining in the same area
throughout the year.
Most samples of Mexican spotted owls
studied using radiotelemetry appear to have
some individuals who are either migratory or
nomadic in winter, but this generally represents a
minority of the population. For example, Willey
(1993:15) reported that two of 11 (18.2%)
radio-tagged owls on the Colorado Plateau RU
migrated during winter. Both apparently left the
breeding area during October and returned
during February. One moved up in elevation to
winter in coniferous forest, whereas the other
wintered in mountain shrub habitat. Both owls
moved 20-25 km between breeding season
ranges and winter ranges.
In the Upper Gila Mountains RU, two of
eight owls (25%) in one study (Ganey and Balda
1989b) and 2 of 13 (15.4%) in another (Ganey
and Block unpublished data) migrated during
the winter. All left the breeding-season range
between November and January, and returned in
March or April. Wintering areas of two owls
were never located. The remaining two owls
migrated approximately 50 km, from ponderosa
pine-Gambel oak forest at approximately 2290
m (7500 ft) in elevation to pinyon-juniper
woodland at approximately 1370 m (4490 ft) in
elevation (Ganey et al. 1992, Ganey and Block
unpublished data). The wintering area was
located in the Basin and Range-West RU,
providing evidence that some individuals may
move seasonally between RUs.

10
Table Table 4.4. 4.4. Use of forest types for foraging by radio-tagged Mexican spotted owls on three study areas in northern Arizona. Data summarized from
Ganey and Balda (1994).
FPO

In the Basin and Range-East RU, neither
Zwank et al. (1994, n = 9 owls) nor Ganey and
Block (unpublished data, n = 15 owls) observed
migration during the nonbreeding season, but
two of eight radio-tagged owls (25%) in another
study moved during the winter. These owls
moved downslope from mixed-conifer forests to
the interface between pinyon-juniper woodland
and desert scrub (Roger Skaggs, New Mexico
State Univ., Las Cruces, NM; pers. comm.).
PATTERNS PATTERNS OF OF HABITAT HABITAT USE USE AT
AT
THE THE STAND STAND SCALE
SCALE
Limited data were available on habitat use by
Mexican spotted owls at the stand scale during
preparation of this Recovery Plan. Analysis of FS
data for some nesting stands in the Upper Gila
Mountains and Basin and Range-East RUs
suggests that owls typically nest in relatively
dense stands with high basal areas of live trees, a
FPO
wide range of tree sizes, suggesting an unevenaged
structure (Figure 4.1), and a large tree
component (Table 4.5). The data were also used
to estimate diminution quotients, or q-factors,
for nesting stands in both RUs (Table 4.5). This
parameter is useful in uneven-aged management
of timber stands. It describes the ratio of number
of trees in any diameter class to the number in
the next-lowest diameter class, and thus describes
the relative shape of the diameter distribution
(Daniel et al. 1979). In both RUs, q-factors
averaged

12
Table Table 4.5. 4.5. Selected characteristics of nest stands of Mexican spotted owls in the Upper Gila Mountains (n = 13 stands) and Basin and Range-East
(n = 44 stands) Recovery Units. Data from the stand data bases for the Apache-Sitgreaves (Upper Gila Mountains) and Lincoln (Basin and Range-East)
National Forests. Values shown are means; no estimates of variability among stands were available.
FPO

Nest Nest Sites Sites
Sites
Armstrong et al. (1994) and Arizona Game
and Fish Department (unpublished data)
sampled habitat characteristics at nest sites on
the Apache-Sitgreaves National Forest, Upper
Gila Mountains RU (Table 4.6). They sampled
both tree and cliff nests, but the majority of
nests sampled were in trees. While limited in
scope, their results suggest that owls typically
nested in large trees in closed-canopy stands.
Ruess (1995) documented current stand
structure on 0.04-ha (0.1-ac) plots at 11 nest
and 9 roost sites representing an unknown
number of owl pairs in ponderosa pine-Gambel
oak forest in northcentral Arizona. He also
attempted to estimate what these sites would
have looked like in terms of forest structure in
1876, before effective fire suppression began in
this area, using methods developed by
Covington and Moore (1994). With a few
exceptions, Ruess (1995) pooled roost and nest
sites when presenting data. Thus, both site types
will be discussed together here.
Comparisons of current and estimated
presettlement conditions on these sites suggest
that pronounced increases have occurred in tree
density, basal area, and canopy cover. Current
density of trees above breast height averaged
1708.8 ± 1009.1 (SD) trees/ha (691.8 ± 408.5
trees/ac), versus an estimated presettlement
density of 0-225 trees/ha (0-91 trees/ac; [Ruess
1995:12, no mean presented]). Current basal
area averaged 66.7 m 2 /ha (290.7 ft 2 /ac; [Ruess
1995:12, no estimate of variability provided]),
versus an estimated average basal area of 17.8
m 2 /ha (77.6 ft 2 /ac; [Ruess 1995:12, no estimate
of variability provided]) circa 1876. Canopy
cover, modeled based on projection of mapped
tree crowns, was estimated at 44.8 ± 12.9% at
present, versus 2.2 ± 2.9% circa 1876 (Ruess
1995:22). Variability in species composition and
structural variables was relatively high for both
estimated 1876 conditions and current conditions.
Two detailed treatments of nesting habitat of
the Mexican spotted owl are currently available
(SWCA 1992, Seamans and Gutiérrez in press).
Seamans and Gutiérrez (in press) compared
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13
Mexican Spotted Owl Recovery Plan
habitat characteristics between 27 plots (0.04 ha;
0.1 ac) centered on nest trees and 27 random
plots from throughout their study area (Tularosa
Mountains, Gila National Forest, New Mexico;
Upper Gila Mountains RU). The nest plots
represented nest sites of 27 pairs of owls. Random
plots were centered on a randomly-selected
tree ³27.3 cm diameter at breast height (dbh),
the minimum diameter among the 27 nest trees.
This was an attempt to minimize the potential
bias associated with centering nest plots on large
trees and random plots on trees of any size.
Owls nested in mixed-conifer/oak forests
more than expected by chance, and in pine-oak
and pinyon-juniper forests less than expected
(Seamans and Gutiérrez in press: fig. 1). Most
nests were located on the lower third of slopes,
and the mean slope aspect at nest sites was
northerly. Nest plots differed significantly from
randomly-located plots within the study area for
a number of variables (Table 4.7). In a discriminant
function analysis, nest plots were best
separated from random plots by variance in tree
height, canopy closure, and basal area of mature
trees (defined as stems >45.8 cm dbh); all were
greater on nest than on random plots (Table
4.7). Cross-validation analyses indicated that the
results of the discriminant analysis were stable,
and the discriminant function successfully
classified 84.6% of a sample of 13 owl nest sites
from other mountain ranges outside the study
area (Seamans and Gutiérrez in press).
Seamans and Gutiérrez (in press) also compared
nest plots to 27 plots randomly located
within nest stands. Nest plots did not differ
significantly from random plots within the same
stand.
SWCA (1992) sampled habitat characteristics
at 84 nests on FS lands in Arizona and New
Mexico. They sampled habitat characteristics
within circular plots (0.2 ha; 0.5 ac), each
centered on and including either a nest tree, a
randomly selected tree within the nest stand, or
a randomly selected tree in a stand within 0.8
km (0.5 mi) of the nest. These will be referred to
as nest, nest-stand, and random-stand plots.
SWCA (1992) concluded that owls selected nest
sites based primarily on the availability of a
suitable nest tree. Hardwood snag basal area and
canopy cover also emerged as potentially impor-

14
Table Table 4.6. 4.6. Habitat characteristics sampled at Mexican spotted owl nest sites on three Ranger districts, Apache-Sitgreaves National Forest, Upper Gila
Mountains Recovery Unit. Shown are means and standard errors (in parentheses). Nests sampled were found in trees (n = 30) or on cliffs (n = 4); some
variables are relevant to only one of the two situations.
FPO

Table Table 4.7. 4.7. Habitat characteristics at Mexican spotted owl nest (n = 27) and randomly located sites
(n = 27) in the Tularosa Mountains, New Mexico; Upper Gila Mountains RU. Shown are means and
standard deviation (in parentheses). Data from Seamans and Gutiérrez (in press).
tant factors in their analysis. This data set was
reanalyzed by both Zhou (1994) and the Team,
using different methods. These reanalyses are
discussed below.
Reanalysis Reanalysis Reanalysis of of SWCA SWCA (1992) (1992) by by by Zhou Zhou Zhou (1994)
(1994)
Zhou (1994) conducted three, two-group
linear discriminant function analyses between
nest, nest-stand, and random-stand plots. He
concluded (Zhou 1994:96-102) that:
1. Mexican spotted owl nest stands differed
from randomly-selected stands in the
vicinity. Nest stands typically had a wide
range of tree diameters and heights, large
maximum tree diameter, and high tree
basal area. Nest stands also had higher
species richness than random stands.
2. Mexican spotted owls also selected for
microsites within nest stands. Nest plots
were located on steeper slopes, had
greater live tree basal area, and were more
likely to be found on north or east
aspects than nest-stand plots.
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15
Mexican Spotted Owl Recovery Plan
3. Diameter and height distributions had
similar shapes on all three plot types, but
the spread of the distribution differed
among plot types. With respect to
diameter distributions, the nest and neststand
plots had greater percentages of
large trees. With respect to tree height,
nest and nest-stand plots had greater
spread to the distribution than randomstand
plots. This wider spread suggests a
tendency for the owl to nest in multistoried
stands, as wider spread to the
height distribution increases the probability
that the stand is multi-storied.
4. Mexican spotted owls nested in large
trees. The mean nest tree was located in
the 92nd diameter percentile and the
79th height percentile.
5. The linear combination of habitat
variables was more successful in classify
ing habitat than reliance on interpretation
of coefficients for single variables.

Reanalysis Reanalysis of of SWCA SWCA (1992) (1992) by by the
the
Recovery Recovery Team
Team
The Team also reanalyzed the data from
SWCA (1992). The Team was interested in
patterns of habitat use within particular geographic
regions, and in how similar nest sites
were among regions. This reanalysis was restricted
to sites in the Upper Gila Mountains
and Basin and Range-East RUs because these
were the only RUs well represented among nests
sampled (n = 44 and 26 sites, respectively).
Because sample sizes were small, sites were
pooled among habitat types within each RU.
Habitat characteristics were first compared
among plot types within RUs, to see if nest sites
differed from nest stands or locally-available,
randomly-selected stands. Characteristics of nest
plots were next compared between RUs, to see
how similar nesting habitat was in different
geographic areas.
We used chi-square tests to evaluate differences
in tree species composition between plot
types (and/or RUs), and Kolmogorov-Smirnov
tests to compare diameter distributions. Because
the Kolmogorov-Smirnov test compares only
two groups at a time, three separate tests were
necessary to compare all three plot types. To
avoid inflating the Type I error rate, we partitioned
the error among these three comparisons
using a Bonferroni adjustment, and used an
alpha level of P 12 cm (4.7 in) dbh, basal area
(m 2 /ha) of live trees and snags >12 cm dbh, and
volume of logs (m 3 /ha) >12 cm in large-enddiameter.
Basal area was calculated for each
individual tree or snag based on dbh, then
summed within each plot. Log volume was
calculated using diameter and length measures,
assuming a cylindrical shape. Log volumes are
overestimated (perhaps greatly) because diameter
was measured at the large end.
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16
Mexican Spotted Owl Recovery Plan
Comparisons omparisons Within ithin ithin R RReco
R Reco
eco ecover eco er ery ery
y U UUnits.—
U nits.— nits.—Tree nits.—
species composition differed significantly among
plot types in both RUs. In the Upper Gila
Mountains RU, nest plots contained greater
proportions of Douglas-fir and Gambel oak and
less ponderosa pine than did random-stand plots
(Figure 4.2). In the Basin and Range-East RU,
nest and nest-stand plots contained more white
fir and less ponderosa pine than did randomstand
plots (Figure 4.2).
Diameter distributions in both RUs were
significantly different between nest plots and
both nest-stand and random-stand plots, but
were not significantly different between neststand
and random-stand plots. Nest plots typically
had lower proportions of basal area in the
smallest size classes than did random-stand plots
(Figure 4.3). In general, basal area was more
evenly distributed across size classes in nest
stands than in random stands, suggesting a trend
toward uneven-aged stands. This trend was more
evident in the Basin and Range-East RU than in
the Upper Gila Mountains RU. Grouping of
trees into four diameter classes, representing
“young,” “mid-aged,” “mature,” and “old” trees
(USDA Forest Service 1993), also indicates that
nest plots contained relatively fewer trees in the
smallest size class and more trees in the largest
two size classes than other plots (Table 4.8a, b;
note that these comparisons refer to percentages
of total trees, not to absolute numbers). In both
RUs, nest trees were significantly larger
(P

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Mexican Spotted Owl Recovery Plan
Figure Figure 4.2a. 4.2a. Tree species composition within nest- and random-stand plots. Data reanalyzed from
SWCA (1992). Upper Gila Mountains Recovery Unit (n = 44 sites).
17

Figure Figure 4.2b. 4.2b. 4.2b. Basin and Range-East Recovery Unit (n = 26 sites).
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18
Mexican Spotted Owl Recovery Plan

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Mexican Spotted Owl Recovery Plan
Figure Figure 4.3. 4.3. Diameter distributions of live trees sampled on nest, nest stand, and random stand plots.
Shown is percentage of total live tree basal area by 4 in (10 cm) size classes for (a) (a) Upper Gila Mountains,
and (b) (b) Basin and Range-East. Data reanalyzed from SWCA (1992).
19

log volume, both nest plots and nest-stand plots
differed from random-stand plots, but not from
each other (Table 4.8a).
Of the five characteristics discussed above,
only live tree basal area and log volume differed
significantly (P = 0.0121 and 0.0061, respectively)
between plot types in the Basin and
Range-East RU (all other P values >0.05). Both
variables differed only between nest plots and
random-stand plots, not between nest plots and
nest-stand plots or between nest-stand and
random-stand plots (Table 4.8b).
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Mexican Spotted Owl Recovery Plan
Table Table 4.8a. 4.8a. Habitat characteristics sampled at 44 Mexican spotted owl nest sites in the Upper Gila
Mountains Recovery Unit, as well as at randomly located plots within the nest stand and in a randomly
selected stand within 0.5 mi of the nest site. Data reanalyzed from SWCA (1992). Values shown are
mean (± standard deviation).
FPO
20
Comparisons omparisons Betw Between Betw een R RReco
R eco ecover eco er ery er y UU
Units.— UU
nits.— nits.— nits.—Species
nits.—
composition of nest sites differed significantly
between RUs (C2 = 1669, df = 4, P

Roost Roost sites sites
sites
Many studies have described characteristics
of roost sites. Some of these descriptions are
based on plot-level sampling, whereas others are
based on sampling of microsites (such as an
individual tree). Microsite descriptions will be
discussed under “Patterns of Habitat Use at the
Tree scale”; plot-level data are discussed below.
In most of the studies described here, the
number of plots measured exceeded the number
of owls studied. Thus, these plots cannot be
considered totally independent samples, and
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Mexican Spotted Owl Recovery Plan
Table Table 4.8b. 4.8b. 4.8b. Habitat characteristics sampled at 26 Mexican spotted owl nest sites in the Basin and
Range-East Recovery Unit, as well as at randomly located plots within the nest stand and in a randomly
selected stand within 0.5 mi of the nest site. Data reanalyzed from SWCA (1992). Values
shown are mean (± standard deviation).
FPO
21
apparent levels of significance may be inflated
(Hurlbert 1984). In most cases, significance
levels are so high that we believe pseudoreplication
is not a major problem. This is further
suggested by the fact that results are comparable
between these studies and another (Seamans and
Gutiérrez in press) that did not involve pseudoreplication
(see below).
Rinkevich (1991; see also Rinkevich and
Gutiérrez in review) and Willey (1993) sampled
habitat characteristics within roost-centered
circular plots of 0.04 ha (0.1 ac) each within the
Colorado Plateau RU. All roost sites were

located in narrow gorges and/or canyons.
Rinkevich (1991) used discriminant function
analysis to compare owl roost sites to randomly
located sites in Zion National Park, Utah. Owl
sites had higher absolute humidity, more vegetation
strata, narrower canyon width, and higher
percent ground litter than random sites
(Rinkevich and Gutiérrez in review). She also
compared randomly located plots (n = 54)
within canyons where owls were heard to plots
(n = 44) within canyons where owls were not
heard. Canyons occupied by owls had higher
humidity and snag basal area than canyons
where owls were not heard (Rinkevich and
Gutiérrez in review). The number of plots in
these analyses is greater than the number of owls
(or canyons in the second analysis), which is
unknown.
Willey (1993) sampled habitat characteristics
on 129 plots representing roost sites of 14 radiotagged
owls on three study areas in southern
Utah. Habitat features at roost sites were compared
to characteristics measured at 30-50
random points scattered within each home range
(Willey 1993:10). Seven variables were analyzed
using discriminant function analysis (Willey
1993:10). Temperature, slope, vegetation canopy
cover, and number of ledges and fir trees discriminated
between roosting plots and random
plots (Willey 1993: table 5). Univariate analyses
provided similar results, suggesting that “owls
used narrow canyon roosts characterized by cool
daytime temperatures, steep slopes, and relatively
dense overhead cover. Roosts typically possessed
large trees in juxtaposition with caves and ledges,
providing a more complex habitat architecture
than the surrounding habitat” (Willey 1993:16).
The number of plots also exceeded the number
of owls in this study.
Ganey (1988, see also Ganey and Balda
1994) sampled habitat characteristics on 167
circular plots (0.04 ha; 0.1 ac) within four owl
home ranges (defined using the MCP method)
in the Upper Gila Mountains RU. Plots represented
high-use roosting and foraging sites, and
randomly-selected sites within owl ranges. This
study also had more plots than owls. In addition,
roost plots were always tree-centered, whereas
only some foraging and randomly-selected plots
were tree-centered. This could create a positive
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Mexican Spotted Owl Recovery Plan
bias for tree-related variables, such as tree density,
tree basal area, and canopy cover, on roost
plots.
Plot type was misclassified 33% of the time
in a 3-group discriminant function analysis
(Ganey 1988; all classification rates refer to
jackknifed classification). Most misclassification
occurred between foraging and roosting sites.
Two-group analyses had higher rates of successful
classification and were easier to interpret. The
function that resulted in maximum separation of
roosting and foraging sites correctly classified
76% of the sites. Variables entering the equation
were canopy closure and snags/ha; both were
greater on roosting sites (Table 4.9). A comparison
of foraging and random sites resulted in
84% successful classification. Variables entering
the discriminant function were total basal area
and big down logs/ha (defined as logs >30.5 cm
[12.0 in] in diameter); both were greater on
foraging sites. Comparing roosting and random
sites, 90% of all sites were successfully classified.
Variables entering the discriminant function
were total basal area, snags/ha, canopy closure,
and big down logs/ha; all were greater on roosting
sites.
Using data from the plots sampled by Ganey
(1988), the Team conducted Kolmogorov-
Smirnov tests on diameter distributions as
described under nest sites (see above). We found
no difference in diameter distributions between
roosting sites and either foraging or random
sites. Diameter distributions were significantly
different between foraging and random sites. In
general, foraging sites had fewer small trees and
more trees in the largest size classes than random
sites (Table 4.9). Again, note that these are
relative comparisons, and refer to percentages of
total trees rather than to absolute numbers of
trees.
Seamans and Gutiérrez (in press) compared
habitat characteristics sampled on 0.04-ha (0.1ac)
circular plots at 78 roost sites and 71 random
sites, Tularosa Mountains, Upper Gila Mountains
RU. Roost plots were centered on the roost
tree (one plot each from 78 separate owls), and
random plots were centered on randomlyselected
trees throughout the study area. Owls
roosted in mixed-conifer/oak forest more than
expected by chance, and in pine-oak forest and

23
Table Table 4.9. 4.9. Habitat characteristics sampled on 0.04 ha (0.1 ac) circular plots within home ranges of radio-tagged Mexican spotted owls inhabiting
mixed-conifer and ponderosa pine forests, northern Arizona (Upper Gila Mountains Recovery Unit). Data from Ganey and Balda (1994); n = six
owls occupying four home ranges. Shown are means and standard deviations (in parentheses).
FPO

pinyon-juniper woodland less than expected.
Most roosts were located on the lower third on
slopes. Roost sites differed significantly from
random plots for several variables (Table 4.10).
Roost sites were best separated from random
sites in a discriminant function analysis by
canopy closure and height variance; both were
greater on roost than on random sites. Crossvalidation
analyses indicated that the discriminant
analysis results were stable (Seamans and
Gutiérrez in press).
A. Hodgson and P. Stacey also evaluated
roost sites in the Upper Gila Mountains RU
(Peter Stacey, Univ. of Nevada, Reno, NV; pers.
comm.). They compared habitat characteristics
sampled on 0.04-ha (0.1-ac) circular plots
between 55 roost sites and 69 random sites in
the San Mateo Mountains, New Mexico (the
number of plots is also greater than the number
of owls in this study). Owls typically roosted in
or near canyon bottoms, in relatively dense
stands of mixed-conifer forest containing significantly
more Douglas-fir, Gambel oak, and
limber pine than random sites. Deciduous trees
accounted for >28% of total basal area and
>50% of total tree density. Roost trees averaged
31 cm (11.6 in) dbh, with most roosting occurring
in Douglas-fir (54%) or Gambel oak (21%).
In a second comparison, Hodgson and
Stacey restricted their analysis to roost and
random sites in mixed-conifer forest (n = 55 and
36, respectively). Within this forest type, roost
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Mexican Spotted Owl Recovery Plan
Table Table 4.10. 4.10. Habitat characteristics at Mexican spotted owl roost (n = 78) and random sites in the
Tularosa Mountains, New Mexico; Upper Gila Mountains RU. Shown are means and standard
deviations (in parenthesis). Data from Seamans and Gutiérrez (in press).
FPO
24
sites contained greater densities and basal areas
of Gambel oak and lower densities and basal
areas of conifers than random sites. Differences
between roost and random sites were generally
greatest with respect to trees from 15-30 cm
(5.9-11.8 in) dbh. Roost sites had greater densities
of deciduous trees and lower densities of
coniferous tree in this size-class than random
plots within mixed-conifer forest (Peter Stacey,
Univ. of Nevada, Reno, NV; pers. comm.).
Tarango et al. (1994) sampled seven roost
sites in Chihuahua, Mexico (Sierra Madre
Occidental-Norte RU), using 0.04-ha (0.1-ac)
circular plots. Roosts were typically located in
multi-layered pine-oak forests on the lower
portions of north-facing slopes. Oaks dominated
most roost sites by density, comprising 46.6% of
the trees present, on average (Tarango et al.
1994:1).
Foraging Foraging Sites
Sites
The only available data on foraging sites
come from Ganey (1988) and Ganey and Balda
(1994), discussed above. Relative to random
sites, foraging sites within owl home ranges had
greater total basal areas and more big down logs/
ha (Table 4.9). Relative to roosting sites, foraging
sites had lower canopy closure and fewer
snags/ha (Table 4.9). In a discriminant function
analysis, foraging sites were not as readily distinguished
from random sites as roosting sites and

were also more variable along a discriminant
function axis (Ganey 1988, fig. 12). Both of
these results suggest greater variability in foraging
habitat than in roosting habitat, consistent
with results at the home-range scale (Ganey and
Balda 1994). As noted above for roosting sites,
foraging sites sampled in this study represented
intensively used habitat and probably do not
represent the full range of conditions used for
foraging.
PATTERNS PATTERNS OF OF HABITAT HABITAT USE
USE
AT AT A A TREE TREE SCALE
SCALE
Several studies have examined characteristics
of trees and other microsites, such as cliff ledges
or caves, used by owls for nesting or roosting.
This information is primarily descriptive, and
with the exception of SWCA (1992), Ruess
(1995), and Seamans and Gutiérrez (in press)
provides no basis for comparing used and available
trees.
Nest Nest Trees
Trees
Nest trees were described, with varying levels
of detail, by SWCA (1992), Armstrong et al.
(1994), Fletcher and Hollis (1994), Ruess
(1995), Seamans and Gutiérrez (in press), and
Arizona Game and Fish Department (unpublished
data). All of these studies were conducted
on FS lands in Arizona and New Mexico, and
some nests may be represented in ³2 studies.
SWCA (1992) sampled 84 nest trees; 81%
were conifers and 19% were hardwoods. Fifty
percent of all nests were in Douglas-fir trees,
with 20% and 19% occurring in Gambel oak
and white fir, respectively (SWCA 1992:17).
Eight percent (n = 7) of all nests occurred in
snags; five of these (57%) were Gambel oak
snags (SWCA 1992:17).
Nest trees averaged 63.3 cm (24.9 in) dbh,
and ranged from 17-127 cm (6.7-50.0 in;
SWCA 1992). Nest structures in living oak trees
(n = 14, 17%) were located either in a broken
top (n = 3) or a side cavity (n = 11). Nest structures
in live conifers included broken top cavities
(n = 5), old raptor nests (n = 14), witches
brooms (n = 25), stick platforms on “bayonet
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Mexican Spotted Owl Recovery Plan
limbs” (n = 12), stick nests in a multiple-topped
tree (n = 4), and a squirrel nest (n = 1). All snag
nests were either broken top (n = 5), or cavity
(n = 3), and one snag contained both nest types
(SWCA 1992:21).
Nest trees were significantly more likely to
have a deformed crown than randomly-selected
trees (SWCA 1992:30), although 65% of all nest
trees had a normal crown form. Types of deformed
crown included broken top (19%),
multiple top (5%), dead top (10%), and dying
top (1%). These percentages are based on 81
nest trees, with three unaccounted for (SWCA
1992: table 9).
Fletcher and Hollis (1994) reported on
microsite characteristics of 248 nests located
during FS inventory and monitoring activities
throughout Arizona and New Mexico. It is
impossible to tell how many different pairs of
owls these nests represent, and some of these
sites may also be included in samples discussed
elsewhere (SWCA 1992, Ruess 1995, Seamans
and Gutiérrez in press). Furthermore, not all
nests could be assigned to a particular Recovery
Unit, limiting regional analyses. Therefore, we
simply summarize some general patterns resulting
from this data set. In many cases, the numbers
presented here were recalculated from
summary data in Fletcher and Hollis (1994). In
those cases the page or figure number where the
data were found is cited. Sample sizes vary
among values reported, because not all variables
were sampled at each site.
Of the 248 nests sampled, 90.3 and 9.7%
were in trees and cliffs, respectively (Fletcher and
Hollis 1994: fig. 28). Most nests fell within a
fairly narrow elevational band, with 72% falling
between 1982 and 2287 m (6500-7500 ft),
85.4% falling between 1982 and 2591 m (6500-
8500 ft), and 95.5% falling between 1829 and
2591 m (6000-8500 ft), respectively (Fletcher
and Hollis 1994: fig. 29). Forty-three percent of
the cliff nests were found below 1982 m (6500
ft).
Almost 50% of 236 nests where aspect was
recorded were located on north or northeast
aspects (Fletcher and Hollis 1994:48). Slope
averaged 44 ± 40 (SD)%, with 34.5% of all
nests found on slopes >40% (Fletcher and Hollis
1994:49). Almost half of all nests were located

on the lower third of slopes, with the remainder
split almost evenly between middle and upper
slopes (Fletcher and Hollis 1994: fig. 50).
Roughly 50% of the nests on upper slopes were
cliff nests or nests in Gambel oak (Fletcher and
Hollis 1994: fig. 50).
Dominant cover types recorded at 237 nest
sites were: 80.2% mixed-conifer, 15.2% pineoak,
2.1% ponderosa pine, 1.7% riparian, and
0.8% other (Fletcher and Hollis 1994: fig. 35).
Of 224 tree nests, 57% were in Douglas-fir, 16%
in Gambel oak, 13% in white fir, 9% in ponderosa
pine, and 5% in other species (Fletcher and
Hollis 1994: fig 40).
Nest tree diameter was recorded at 204 nest
sites. Trees < 15.2 cm (61 cm (>24 in) dbh (Fletcher and Hollis
1994: fig. 41). Forty-five percent of tree nests
were classified as “witches broom”, with 31.3%
in cavities (including broken tops), 14.7% in
“debris platforms”, and 8.9% in “other stick
nests” (Fletcher and Hollis 1994: fig. 36).
Six of 11 nests (54.5%) sampled by Ruess
(1995: fig 7) were in Gambel oak, with the
remainder in ponderosa pine. Ruess (1995) did
not report mean diameters for nest trees, but
found four nests (36.4%) in trees of
presettlement origin (>115 yrs in age) despite
the fact that such trees accounted for only 0.5%
of total trees on his study area (Ruess 1995: table
3, fig. 7).
Seamans and Gutiérrez (in press) reported
78% of 27 nests in Douglas-fir, 11% in white fir,
7% in ponderosa pine, and 4% in southwestern
white pine. With respect to nest structure, 61%
were located in dwarf mistletoe infections,
10.5% in old squirrel nests, 10.5% in old raptor
nests, 7% in debris collections, 7% in tree
cavities, and one nest (4%, n = 28 nests for these
calculations) was on a cliff. Nest trees averaged
60.6 ± 22.4 cm (23.9 ± 17.6 in) in dbh and
164 ± 44.8 years in age. Nest trees were significantly
larger and older than randomly sampled
trees within the nest vicinity (Seamans and
Gutiérrez in press).
Volume II/Chapter 4
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Roost Roost Trees
Trees
Mexican Spotted Owl Recovery Plan
Several researchers have described characteristics
of roost trees and a very small area around
them. Results are summarized by study area and
RU, where possible, in Table 4.11. In general,
roost characteristics appeared to be relatively
variable among study areas (Table 4.11), suggesting
that greater variability exists among roost
trees than among trees used for nesting. Canopy
closure was more consistent among study areas
than most other characteristics sampled, and was
relatively high on most study areas. Canopy
closure was 85% of
the roost sites sampled on that study area were
located on cliffs or in pinyon-juniper woodland
(Table 4.11a).
Roost tree characteristics appeared to be
relatively similar among similar habitat types.
For example, mean roost tree diameter was more
consistent among the mesic mixed-conifer sites
(San Francisco Peaks, White Mountains, and
Sacramento Mountains: mixed-conifer) than
between these sites and other areas. Similarly,
characteristics were more similar among the
more xeric sites (Sacramento Mountains: xeric
mixed forest and Bar-M watershed) than between
these and other areas (Table 4.11). One
clear pattern that emerges from these studies is
that owls roost in smaller trees, on average, than
those used for nesting. Ruess (1995: fig. 7),
however, noted that three of nine roosts observed
in ponderosa pine-Gambel oak forest
were >115 yrs old, despite the fact that only
0.5% of all trees sampled in the area were of
such age (Ruess 1995: Table 3). This suggests
that old, large trees may also be important for
roosting in some areas.
Fletcher and Hollis (1994) reported summary
characteristics sampled at 433 roost sites
located during FS inventory and monitoring
efforts in Arizona and New Mexico. This sample
is discussed separately here because roost sites
could not generally be assigned to particular
RUs, as was done for the data sets summarized in
Table 4.11. This data set is subject to all the

Volume II/Chapter 4
Mexican Spotted Owl Recovery Plan
Table Table 4.11a. 4.11a. Selected characteristics of roost sites used by radio-tagged Mexcan spotted owls in the
Colorado Plateau Recovery Unit. Values shown are means (± standard deviation) for continuous
variables, % for categorical variables. Source: D.W. Willey (unpublished data).
FPO
27

Volume II/Chapter 4
Mexican Spotted Owl Recovery Plan
Table Table 4.11b. 4.11b. Selected characteristics of roost sites used by radio-tagged Mexican spotted owls in the
Upper Gila Mountains Recovery Unit. Values shown are mean (± standard deviation) for continuous
variables, % for categorical variables.
FPO
28

Volume II/Chapter 4
Mexican Spotted Owl Recovery Plan
Table Table 4.11c. 4.11c. Selected characteristics of roost sites used by radio-tagged Mexican spotted owls in the
Basin and East-Range Recovery Unit. Values shown are mean (± standard deviation) for continuous
variables, % for categorical variables.
FPO
29

limitations discussed relative to nest sites (see
above) described by Fletcher and Hollis (1994).
Ninety-five percent of all roosts were in
trees, with the remainder on cliffs or in caves
(Fletcher and Hollis 1994: fig. 42). Percent slope
averaged 46 ± 34%, with 45% of all roost sites
occurring on slopes >40% (Fletcher and Hollis
1994: fig. 46). Most (57%) of these roost sites
were found on the lower third of slopes (Fletcher
and Hollis 1994: fig 47).
Of 367 roost sites where cover type was
recorded, 65.7% were in mixed-conifer, 27.2%
in pine-oak, 2.7% in riparian, 1.4% in ponderosa
pine, and 3.0% in other cover types
(Fletcher and Hollis 1994: fig. 49). A variety of
trees provided roost perches, including Douglasfir
(38.3%), Gambel oak (17.9%), ponderosa
pine (11.9%), white fir (11.4%), other oak
species (8.0%), and other species (12.4%;
Fletcher and Hollis 1994: fig. 53; n = 402). Trees
24 in) in dbh, respectively
(Fletcher and Hollis 1994: fig. 54).
Ganey and Block (unpublished data) evaluated
seasonal differences in roost site characteristics
in ponderosa pine-Gambel oak forest (Table
4.12). Canopy closure was greater at roosts used
during the breeding season. Owls used Gambel
oak significantly more often during the breeding
season, and tended to roost more often on the
upper third of slopes during the breeding season
and on the middle third during the nonbreeding
season.
Ganey and Block (unpublished data) also
reported some characteristics of winter roosts
used by two owls that migrated to lower elevations
(Table 4.13). Both owls roosted primarily
in pinyon-juniper woodland, on the middle and
upper portions of slopes. They typically perched
low in short juniper trees, well hidden by dense
foliage and near the center of the tree. These
winter roosts differed greatly in structure and
species composition from typical summer
roosting habitat.
Volume II/Chapter 4
30
Mexican Spotted Owl Recovery Plan
WINTERING WINTERING HABITAT HABITAT
HABITAT
Present knowledge of wintering habitat of
Mexican spotted owls comes primarily from
radiotelemetry studies (see Patterns of Habitat
Use at the Home Range Scale) and opportunistic
observations of wintering adults. Radiotelemetry
studies indicate that many owls remain on their
breeding areas throughout the year, whereas
some migrate off of the study area. Where
wintering areas of migrants have been located,
they are typically in lower elevation woodland or
scrub habitats with more open structure than
typical breeding habitat. However, one owl in
the Colorado Plateau RU migrated upwards in
elevation to winter in coniferous forest (Willey
1993).
Opportunistic sightings of spotted owls
during the winter also suggest that part of the
population moves to lower elevations. For
example, owls have been sighted in lower Sabino
Canyon, outside of Tucson, Arizona, and on golf
courses in Tucson in recent winters (Russell
Duncan, Southwestern Field Biologists, Tucson,
AZ, pers. comm.). An adult owl banded on the
Gila National Forest, Upper Gila Mountains
RU, was recovered during winter 1995 near
Deming, New Mexico, Basin and Range-East
RU. This bird had apparently traveled approximately
160 km (100 mi) from the area where it
was located during the breeding season, from
high-elevation forest to Chihuahuan desert
(Mark Seamans, Humboldt State Univ., Arcata,
CA, pers. comm.).
In summary, available evidence on wintering
habitat is limited, but suggests that the bulk of
the owl population is nonmigratory. Where
migration does occur, it typically involves
movement to lower, warmer, and more open
habitats. In some cases, migration involves
movement between adjacent Recovery Units.
Little quantitative data exists to describe typical
wintering habitat for either migrants or yearround
residents.
DISPERSAL DISPERSAL HABITAT
HABITAT
Very little is known about habitat use either
by adults during migration or by juveniles

Volume II/Chapter 4
Mexican Spotted Owl Recovery Plan
Table Table 4.12. 4.12. Seasonal roost site characteristics of radio-tagged Mexican spotted owls in ponderosa
pine-Gambel oak forest, Arizona (Upper Gila Mountains Recovery Unit). Data from Ganey and
Block (unpublished). Values shown are mean (± SD) for continuous variables, % for categorical variables.
FPO
31

during dispersal. Willey (1993) monitored seven
dispersing juvenile owls in Utah. These juveniles
apparently moved through a variety of habitat
types, including several that might generally be
considered too open for use by spotted owls.
None of these juveniles survived to reproduce.
A. Hodgson and P. Stacey radio tagged five
juveniles in the San Mateo Mountains, New
Mexico (Upper Gila Mountains RU). Two
juveniles apparently dispersed across open
grassland to the Black Range, but their ultimate
fate is not known (Peter Stacey, Univ. of Nevada,
Reno, pers. comm.). Three other juveniles
apparently remained in the San Mateo Mountains.
No information is available on habitats
used by these owls.
Volume II/Chapter 4
ADDITIONAL ADDITIONAL STUDIES
STUDIES
In addition to the above studies, two additional
studies are treated separately here because
they either were not specific to a single scale
Mexican Spotted Owl Recovery Plan
Table Table 4.13. 4.13. 4.13. Characteristics of roost sites used by two migrant Mexican spotted owls on their winter
range. Both owls bred in ponderosa pine-Gambel oak forest in the Upper Gila Mountains Recovery
Unit, and wintered in pinyon-juniper woodland on the Basin and Range-West Recovery Unit. Data
from Ganey and Block (unpublished).
FPO
32
(Johnson 1989, Dames and Moore 1990) or did
not distinguish between site types (Dames and
Moore 1990). Johnson (1989) compared habitat
characteristics sampled at one roost and one nest
site with characteristics sampled at 20 points
within the same stand. Thus, this provides a
comparison of site characteristics with overall
characteristics of the surrounding stand. Mean
tree height, overstory basal area, understory basal
area, overstory density, and snag density were all
greater at the roost and nest sites than in the
surrounding stand. Despite the greater understory
basal area at roost and nest sites, understory
density was greater within the stand, suggesting
that the understory at the roost and nest sites
contained fewer but larger trees (Johnson
1989:12). Johnson (1989:14-15) further noted
that the roost and nest sites ranked high (relative
to the stand) for evenness indices for both tree
species and diameter, and suggested that smallscale
diversity may be an important factor in

habitat selection by spotted owls (see also
Johnson and Johnson 1988, Johnson 1990).
Dames and Moore (1990) reported on
habitat characteristics in areas occupied by
Mexican Spotted Owls in Arizona and New
Mexico (Upper Gila Mountains and Basin and
Range East-RUs). Sampling methods and
sampled area differed between states (Dames and
Moore 1990:10), and most of the area sampled
was based on owl presence in the area, rather
than on specific evidence of use by owls for
either foraging, roosting, or nesting. Results of
hypothesis tests regarding habitat characteristics
in this study were inconclusive. In both states,
the most consistent feature within and among
areas sampled was variability (Dames and Moore
1990: executive summary).
Volume II/Chapter 4
CONCLUSIONS
CONCLUSIONS
Habitat Habitat Relationships
Relationships
Several patterns are evident upon evaluation
of current knowledge regarding habitat relationships
of Mexican spotted owls. The first is that
most information is limited to relatively fine
spatial scales. For example, we have considerable
information about roost and nest trees, and roost
and nest sites, but have little information on
stands used by owls, habitat composition of owl
home ranges, or landscape configurations used
by spotted owls. Second, most information on
owl habitat use relates to the breeding season,
and to habitats used for nesting and/or roosting.
We know little about habitat use during winter
or dispersal periods, or about what constitutes
adequate foraging habitat. Third, most information
on owl habitat use and selection comes
from correlative studies that do not demonstrate
cause-and-effect relationships. Fourth, our
knowledge of owl habitat-use patterns comes
from a very short time period (mainly 1984present).
All of these factors limit our ability to define
what constitutes spotted owl habitat, or what
desired future conditions should be for spotted
owls. What we can do is describe features of
breeding-season roosting and nesting habitat
used by owls at this time. In most cases, histori-
33
Mexican Spotted Owl Recovery Plan
cal information is not adequate to know whether
currently-occupied sites were also occupied in
the past, or to allow us to draw conclusions
about structural features of habitats used in the
past.
Spotted owls typically nest or roost either in
deep, rocky canyons, or in any of several forest
cover types. The relative use of canyons versus
forests varies among regions. For example, owls
in parts of the Colorado Plateau RU are found
exclusively in deep, rocky canyons, whereas owls
in many other RUs are found primarily in forests
(although these forests are often in canyons).
Where owls occur in forests, they typically
select large, old trees for nesting. Nest and roost
sites are found primarily in mixed-conifer forest
(Table 4.1), although pine-oak forests are also
used in some areas, such as parts of the Upper
Gila Mountains, Basin and Range-West, and
Sierra Madre Occidental-Norte RUs (Table 4.1;
see also Ganey and Balda 1989a, Duncan and
Taiz 1992, Ganey et al. 1992, Fletcher and
Hollis 1994, Tarango et al. 1994, Seamans and
Gutiérrez in press). Nest and roost sites typically
contain structurally-complex, uneven-aged
forests, with a variety of age- and/or size- classes,
a large tree component, many snags and down
logs, and relatively high basal area and canopy
closure (Tables 4.6-4.11; see also SWCA 1992,
Armstrong et al. 1994, Ganey and Balda 1994,
Ruess 1995, Seamans and Gutiérrez in press).
Diversity of tree species and diameters appears to
be high in many owl nesting and roosting areas
(Johnson and Johnson 1988, Johnson 1989,
Johnson 1990, Seamans and Gutiérrez in press).
Many roost and nest sites are found in canyon
bottoms or low on canyon slopes (Table 4.11;
see also Ganey and Balda 1989a, Fletcher and
Hollis 1994, Tarango et al. 1994:36, Seamans
and Gutiérrez in press). Many have a conspicuous
broadleaved component, in the form of
riparian trees or especially various oaks (Ganey
and Balda 1989a, Duncan and Taiz 1992, Ganey
et al. 1992, SWCA 1992, Tarango et al. 1994,
Ruess 1995, Seamans and Gutiérrez in press).
The reasons why spotted owls nest and roost
in structurally-complex, diverse forests and deep
canyons have not been conclusively demonstrated.
Barrows (1981) suggested that owls seek
dense forest stands as protection from high

daytime temperatures. This explanation is
attractive with respect to Mexican spotted owls,
because the most apparent common denominator
between the types of forests and deep, rocky
canyons used is that both situations provide cool
microsites (Kertell 1977, Ganey et al. 1988,
Ganey and Balda 1989a, Rinkevich 1991, Willey
1993). Further, there is some evidence that,
relative to the great horned owl, which is found
in hotter and drier areas, the spotted owl has
difficulty dissipating metabolic heat at high
temperatures (Ganey et al. 1993).
Carey (1985) and Gutiérrez (1985) also
hypothesized that northern spotted owls might
seek dense old, closed-canopy forests because
such areas supported higher prey densities, or
because the owls were better able to avoid
predators in such areas. Present information,
however, suggests that owls forage in a wider
variety of forest types than are used for roosting
(Ganey and Balda 1994, see also Ward and Block
1995). Further, although owls in one study
roosted primarily in unlogged mixed-conifer
forests, they did not show a strong pattern of
selection for such forests when foraging (Table
4.4). This suggests that the association between
spotted owls and mixed-conifer forest may be
driven more by roosting and/or nesting behavior
than by foraging behavior (Ganey and Balda
1994). We currently have no information with
which to test the hypothesis that spotted owls
are better able to avoid predators in complex
forests or deep, rocky canyons.
In summary, at present we suspect that
selection of typical nesting and roosting habitat
is driven primarily by microclimatic considerations.
Prey availability may also be an important
consideration, however, and prey density in and
around an area with microclimatic conditions
typical of nest/roost habitat may determine
whether or not that site is used by owls. Prey
availability may also determine how large an area
owls must use to meet their energetic needs
(Carey et al. 1992, Verner et al. 1992, Zabel et
al. 1995). However, we suspect that the primary
factor limiting spotted owl distribution is the
presence on the landscape of habitat suitable for
roosting and nesting.
In some areas, the types of forests used for
roosting and nesting are primarily restricted to
Volume II/Chapter 4
34
Mexican Spotted Owl Recovery Plan
canyon situations. This is particularly true at
lower elevations, where mixed-conifer forest is
generally found only in canyon bottoms or on
north-facing canyon slopes. Thus, the distribution
of roosting and nesting habitat, and of
spotted owls in these areas, is naturally fragmented
and discontinuous. Opportunities for
increasing the amount of spotted owl habitat in
such areas are limited, and management efforts
would be better focused on preserving and
enhancing habitat where it exists. Replacement
habitat in such areas may need to develop in situ
following stand-replacing disturbances.
In other areas, such as high-elevation mixedconifer
forest, it may be possible to develop
spotted owl habitat over more of the landscape.
An example of such an area is the Sacramento
Mountains (Lincoln National Forest, Basin and
Range-East RU). Spotted owls are abundant and
widely distributed in mixed-conifer forests across
this range (Skaggs and Raitt 1988, Fletcher and
Hollis 1994: fig. 24). Much of this area was
subject to relatively intensive railroad logging
early this century (Glover 1984), but these
forests have recovered quickly and attained
structural complexity (Table 4.8b), demonstrating
that development of replacement habitat is
possible after management under some circumstances.
In areas such as this, managers might
combine protection of existing habitat with
attempts to develop replacement habitat over
time, in a more dynamic approach to habitat
management.
Comparisons Comparisons With With Other Other Subspecies
Subspecies
of of of Spotted Spotted Spotted Owls
Owls
There are many similarities in habitat-use
patterns of the three subspecies (northern,
California, and Mexican) of spotted owls. For
example, all three appear to be most common in
structurally-complex forest environments,
although floristic composition of habitats used
varies both within and between subspecies’
ranges (for other subspecies see reviews in
Thomas et al. 1990, Gutiérrez et al. 1992). Both
the California (Gutiérrez et al. 1992) and Mexican
subspecies most commonly nest in mixedconifer
forest, followed by forest types domi-

nated by oaks or conifers and oaks. Both the
California (Gutiérrez et al. 1992) and Mexican
subspecies appear to use a wider variety of
habitat conditions for foraging than for roosting
and nesting. These consistencies in habitat use
patterns between subspecies occupying different
geographic areas and habitat types further
strengthen our conclusion that spotted owls are
seeking particular types of habitat features for
nesting and roosting.
Habitat Habitat Trends
Trends
Because the listing of the owl was based
partially on projected declines in owl habitat, it
is worth discussing what we know about trends
in owl habitat. The following discussion focuses
separately on various habitat conditions used by
spotted owls. It is largely restricted to trends in
roosting and nesting habitat, because most of
our information relates to such areas, and because
such habitat is thought to limit spotted
owl distribution. Finally, because little historical
information exists with respect to the type of
microsite conditions that describe roosting and
nesting habitat of spotted owls, this discussion is
necessarily largely qualitative.
Rocky Rocky Canyons
Canyons
Mexican spotted owls are found primarily in
rocky canyons in parts of their range, such as
southern Utah (Kertell 1977, Rinkevich 1991,
Willey 1992, 1993, Utah Mexican spotted owl
Technical Team 1994). In other areas, part of the
population also inhabits rocky canyons, but
these are generally more heavily forested than
the slickrock canyons found in parts of the
Colorado Plateau RU (Ganey and Balda 1989a,
USDA Forest Service 1993, Fletcher and Hollis
1994). There is little evidence for change in
habitat quality or loss of habitat in slickrock
canyons. Canyon-bottom vegetation may have
been degraded by grazing in some cases (see
below), and some habitat may have been lost
beneath large reservoirs along the Colorado
River and its tributaries. The latter change could
have decreased connectivity among remaining
populations. Otherwise, we suspect that habitat
Volume II/Chapter 4
35
Mexican Spotted Owl Recovery Plan
trends are relatively stable in areas where owls are
found primarily in slickrock canyons.
Riparian Riparian Forests
Forests
Historically, owls were found in low-elevation
riparian forests (Bendire 1892, Phillips et al.
1964, and possibly Woodhouse 1853). These
forests have undergone extensive modification
because of recreation, flood control, livestock
grazing, and modification of natural water tables
(Knopf et al. 1988; see also Kennedy 1977,
Kauffman and Krueger 1984, Minckley and
Clark 1984, Skovlin 1984, Minckley and Rinne
1985, Platts 1990, Schulz and Leininger 1990,
Dick-Peddie 1993). Collectively, these activities
and other factors have changed the species
composition and structure of riparian forests. In
extreme cases, riparian forests have disappeared
entirely. No breeding spotted owls have been
documented in lowland riparian forests in recent
times. Surveys of such habitat have been far from
exhaustive, and owls may still inhabit some
remnant riparian forests. Nevertheless, the
overall trend with respect to spotted owls breeding
in lowland riparian forest habitat has clearly
been negative.
Spotted owls also commonly occur in
canyon-bottom riparian forests at higher elevations,
interspersed with other forest types. In
many cases these forests have also been degraded
(Schulz and Leininger 1991, see also Fleischner
1994). Management to retain and enhance these
riparian forests would likely be beneficial to
spotted owls (as well as many other plants and
animals).
Coniferous Coniferous Coniferous Forests
Forests
Trends in coniferous forests are more difficult
to evaluate. It is clear that changes have
occurred in southwestern forests. These stem
primarily from three sources: disruption of
natural disturbance regimes, grazing, and timber
harvest. Many decades of fire suppression have
disrupted natural disturbance regimes (Cooper
1960, Madany and West 1983, Stein 1988,
Savage and Swetnam 1990, Covington and
Moore 1992, 1994, Harrington and Sackett
1992, Johnson 1995). The absence of frequent,

low-intensity fire, coupled with widespread
overgrazing by livestock in the late 1800s,
reduced competition between herbaceous
vegetation and tree seedlings. These effects
produced a good seedbed for conifer regeneration,
and generally resulted in increases in tree
densities on forested lands (Rummel 1951,
Madany and West 1983, Zimmerman and
Neuenschwander 1984, Stein 1988, Savage and
Swetnam 1990, Covington and Moore 1992,
1994, Harrington and Sackett 1992, Johnson
1995, Ruess 1995). Such increases in tree density
can not only alter stand structure, but can also
lead to declines in shade-intolerant tree species,
and drive ecological succession from one forest
type to another. For example, some ponderosa
pine forests appear to be converting to mixedconifer
forest.
Timber harvest in many areas has also altered
stand structure and sometimes species composition.
Timber harvest can occur in different
forms, with different intensity, and with different
effects on stand structure. In many cases,
however, the net effect of timber harvest is a
decrease in old trees and at least a short-term
decrease in tree density and basal area. In these
respects timber harvest tends to work opposite
the effects of disruptions in natural disturbance
regimes described above. Where timber harvest
targets shade-intolerant species, however, it
could further the trend of ecological succession
towards shade-tolerant species.
The net effect of these processes on amount
and quality of spotted owl habitat is difficult to
determine. USDI (1993:14251), citing Fletcher
(1990), postulated that spotted owl habitat had
decreased in amount due to timber harvest.
Fletcher and Hollis (1994:29) estimated that
1,068,500 ac of forested habitat in Arizona and
New Mexico had been rendered unsuitable for
spotted owls due to human activities, primarily
timber harvest, through 1993. Conversely, Hull
(1995:7) reported that “thousands of acres have
converted from ponderosa pine to mixedconifer,”
and argued that the amount of Mexican
spotted owl habitat had increased. For several
reasons, we submit that either viewpoint is
difficult to substantiate with presently-available
data.
Volume II/Chapter 4
36
Mexican Spotted Owl Recovery Plan
First, the claim that thousands of acres of
ponderosa pine have converted to mixed-conifer
is unsubstantiated. Johnson (1995: fig.1) shows a
large increase in acreage of mixed-conifer in
Arizona and New Mexico between 1966 and
1986, based on forest inventories conducted in
those years. Johnson (1995:1) also presents
numbers suggesting that much of the increase in
mixed-conifer forest is due to invasion of meadows,
rather than conversion of ponderosa pine
forest. Further, this information is extrapolated
from data presented in the original inventories
(Choate 1966, Spencer 1966, Conner et al.
1990, Van Hooser et al. 1993), and no information
is provided on how that extrapolation was
done. Therefore, it is impossible to assess the
accuracy of the figures presented. Methods and
definitions may also have changed between
inventories. Referring to comparisons between
the 1986 inventory and earlier inventories, Van
Hooser et al. (1993:1) state: “The changes in
definitions and survey standards make detailed
comparisons with previous inventory results
unwise.”
Second, the idea that all mixed-conifer forest
is spotted owl habitat is not supported by the
available data. As noted previously, owls roost
and nest primarily in structurally-complex
forests with particular features, including large,
old trees. Recent invasion of meadows by mixedconifer
forest is unlikely to have created this type
of habitat. If that process proceeds, however, it
could create owl habitat in the future.
Finally, most available data on historical
forest structure and increases in forest density
relate to ponderosa pine forest (USGS 1904,
Woolsey 1911, Harrington and Sackett 1984,
Covington and Moore 1992, 1994). As we have
shown here, this forest type is not typically used
for roosting and nesting by spotted owls. Data
presented by Ruess (1995) suggest that similar
changes have occurred in ponderosa pine-
Gambel oak forest, which is used by spotted
owls. No such data exist for mixed-conifer forest,
however, which is the primary type used by
spotted owls for roosting and especially for
nesting. It seems logical to assume that increases
in density have also occurred within this forest
type. Without quantitative data on changes in
this forest type, however, determining whether

or not such changes have been favorable to
spotted owls is essentially impossible.
In summary, conflicting speculation exists
regarding trends in spotted owl habitat in
coniferous forest. Some authors speculate that
timber harvest has reduced the amount of owl
habitat, whereas others speculate that fire suppression
has increased the amount of owl habitat.
Data presented here suggest that spotted owl
habitat is complex. The types of historical
evidence available do not allow for any clear
analysis of trends in such habitat. We recognize
that we cannot return to the past to collect such
data, but we can learn from this situation. Our
inability to evaluate habitat trends strongly
emphasizes the need for accurate and comprehensive
inventory and monitoring of forest
resources, so that in the future changes in forest
habitat can be assessed over time.
Research Research Research Considerations
Considerations
Clearly, much remains to be learned about
habitat relationships of the Mexican spotted owl.
Gutiérrez et al. (1992) outlined a number of
research considerations relative to habitat relationships
of the California spotted owl. These
are all relevant to the Mexican subspecies as well.
We briefly summarize some additional considerations
here.
Quantitative data on patterns of owl habitat
use are largely or completely lacking for some
geographic regions, habitat types, and spatial
scales. Particularly striking is the lack of quantitative
data on habitat relationships at the stand
and landscape scales. Some estimates of habitat
conditions measured on small plots, such as
canopy closure, may not be representative of
conditions at the stand scale. Further, many
management actions are planned at a stand scale,
and implementation of ecosystem management
approaches will require more attention to habitat
composition and pattern at the landscape scale.
Thus, it seems critical to obtain better information
at these (as well as other) scales. The Team’s
efforts to evaluate habitat use patterns at the
landscape scale were frustrated by the lack of
suitable GIS coverages. Development of such
coverages would greatly facilitate future analyses.
Volume II/Chapter 4
37
Mexican Spotted Owl Recovery Plan
Further, any credible attempts to monitor
amounts of spotted owl habitat or trends in such
habitat will require both better data on what
constitutes spotted owl habitat at various spatial
scales, and better data on forest structure across
the landscape.
Most studies of habitat use-patterns have
been correlative rather than experimental, which
limits our ability to draw conclusions about
habitat selection by Mexican spotted owls.
Further, even where correlates of owl occupancy
have been identified, these characteristics have
not been linked to owl fitness. Demographic
studies of Mexican spotted owls are underway in
a few areas. Far greater efforts will be required to
obtain the data necessary to determine which
habitats or areas contain self-supporting populations,
and to evaluate habitat composition
within those areas.
In the meantime, forest management is
ongoing, and we assume that this will continue.
Although controlled experiments in forest
management are exceedingly difficult to design
and conduct, forest management activities could
provide a great opportunity to learn more about
the response of spotted owls to habitat configurations
at various scales. Experimental silvicultural
prescriptions could be developed and
applied, guided by current knowledge of habitat
conditions. Such knowledge should be supplemented
by studies of owl habitat in other areas
and habitats, and at other scales. McKelvey and
Weatherspoon (1992) provide an example of a
conceptual approach to integrating silviculture
with knowledge of stand structures used by
spotted owls.
Finally, little attention has been paid to the
ecology and habitat relationships of the owl's
principal prey species (but see Ward and Block
1995), and to how forest management might
influence population levels of these species.
Management actions could indirectly affect
spotted owls, either positively or negatively,
through effects on their prey species. Therefore,
these species should also be considered in future
management planning and research activities.

Volume II/Chapter 4
LITERATURE LITERATURE CITED
CITED
Armstrong, J. A., P. C. Christgau, and K.
Fawcett. 1994. Habitat characteristics of
Mexican spotted owl nest sites on the Alpine
Ranger District, Apache National Forest,
Arizona. Draft Report. Arizona Game and
Fish Dept., Phoenix. 102pp.
Barrows, C. W. 1981. Roost selection by spotted
owls: an adaptation to heat stress. Condor
83:302-309.
Bendire, C. E. 1892. Life histories of North
American birds. U.S. Nat. Mus. Spec. Bull. 1.
Block, W. M., and L. A. Brennan. 1993. The
habitat concept in ornithology: theory and
application. Current Ornith. 11:35-91.
Brown, D. E., C. H. Lowe, and C. P. Pase. 1980.
A digitized systematic classification for ecosystems
with an illustrated summary of the
natural vegetation of North America. U.S.
For. Serv. Gen. Tech. Rep. RM-73. Rocky
Mtn. For. and Range Exper. Stn. Fort Collins,
Colo. 93pp.
Byers, C. R., R. K. Steinhorst, and P. R.
Krausmann. 1984. Clarification of a technique
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40
Mexican Spotted Owl Recovery Plan
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Volume II/Chapter 4
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Mexican Spotted Owl Recovery Plan

Volume II/Chapter 5
CHAPTER CHAPTER 5: 5: Mexican Mexican Spotted Spotted Owl Owl Prey Prey Ecology
Ecology
In addition to shelter, water, and other
requirements, habitat must also provide spotted
owls with food. Certain trees within specific
forest communities may meet nesting, roosting,
and perching needs, but the tree component
alone may not necessarily sustain the animal
species upon which the owls prey. Conserving
appropriate habitat for the owl includes conserving
habitat for a suite of prey species.
The distribution and abundance of prey
often influence the distribution, abundance, and
reproduction of raptors (Newton 1979). In
owls, reproductive success is often correlated
with prey abundance (Craighead and Craighead
1956, Southern 1970, Lundberg 1976,
Wendland 1984, Korpimäki and Norrdahl
1991). The postulated mechanism behind this
relationship is energetically based. Male owls
must provide enough food to their female mates
during incubation and brooding to prevent
abandonment of nests or young (Johnsgard
1988). Accordingly, ecologists suspect that
spotted owls select habitats partially because of
the availability of prey (Carey 1985, Thomas et
al. 1990, Verner et al. 1992). Understanding the
natural history of the spotted owl’s primary prey
is vital information for the Recovery Plan because
it provides resource planners and managers
with another tool for evaluating an area’s ability
to support spotted owls.
This section summarizes information about
spotted owl-prey relationships and the ecology of
the owl’s prey. Specifically, our objectives are to:
(1) describe the diet of the Mexican spotted owl;
(2) identify prey that may influence owl fitness;
and (3) quantify habitat correlates of the owl’s
primary prey.
Ideally, relationships among the Mexican
spotted owl, its prey, and the prey’s habitat
should be examined across different spatial and
temporal scales. In reality, the available information
permits only a limited view of the owl’s prey
ecology. For example, we could describe abundance
and distribution of the owl’s common
prey among different vegetation communities,
but could not provide a direct link between owl
James P. Ward, Jr., and William M. Block
1
Mexican Spotted Owl Recovery Plan
habitat use and prey availability. Although the
latter information is preferred for prioritizing
habitat conservation, our approach relies upon
conserving a general mixture of habitats for the
owl and its prey throughout major portions of
the owl’s range. In time, information from more
specific studies should be used to refine the
general findings presented here.
METHODS METHODS FOR FOR
FOR
DETERMINING DETERMINING OWL OWL DIETS
DIETS
The dietary habits of raptors can be determined
both directly and indirectly. Observations
of prey capture and of prey taken to roosts or
nests provide direct evidence of a raptor’s diet.
However, such observations are difficult to
obtain from nocturnal foragers like owls and
offer little opportunity for quantitative analysis.
Regurgitated pellets of undigested materials (fur,
feathers, bones, chitinous exoskeletons) offer an
indirect, alternative method for analyzing the
feeding habits of owls (Errington 1930, Glading
et al. 1943, Marti 1987).
Spotted owl prey are identified by examining
the contents of pellets collected below roosts and
nests. Prey remains are identified to species,
genus, or a less specific prey category and tallied.
Diets are then quantified using two measures,
relative frequency and percent biomass (Forsman
et al. 1984, Marti 1987). Relative frequency of
prey is expressed as the number of individual
items of a given prey species or group divided by
the total number of all individual items found in
a sample. Biomass (g) is the total number of
items of a given prey species or group multiplied
by the average mass (g) for that species or group.
Commonly, both relative frequency and biomass
are expressed as percentages. Both measures can
be used to compare owl diets among sampling
units such as reproductive groups, locations,
seasons, and so on. The two measures provide
different information. Measures of relative
frequency indicate the proportion of each prey
type in the owl’s diet by number, whereas,

percent biomass indicates the proportion of each
prey type by weight.
Pellets may provide biased measures of owl
diets. Pellets are typically collected opportunistically
below roosting owls or from known roost
groves, not randomly or systematically. The bias
potentially resulting from nonrandom sampling
could not be evaluated. We assumed that items
found in pellets reflected the true proportions of
prey species in owl diets. The methods we used
to quantify Mexican spotted owl diet are comparable
to other studies conducted on the northern
and California subspecies (see reviews by Thomas
et al. 1990 and Verner et al. 1992). Accordingly,
we restricted analyses and inferences to
relative comparisons.
We compiled and analyzed prey remains of
Mexican spotted owls as reported in 13 studies
conducted since 1977 (Tables 5.1-5.6). A total
of 11,164 prey items was examined. These data
consisted of 25 data sets from 18 geographic
areas throughout the owl’s range, and included
most published and unpublished information of
Mexican spotted owl diet through 1993 (Tables
5.1-5.6). Kertell (1977) was not used because of
the small number of items reported.
Each data set differed in the number of owls,
years, and pellets examined. In some cases, the
number of owls studied or pellets collected were
not recorded. Thus, we could not use owls as the
sampling unit or separate differences among owl
territories in region-wide analyses. However,
each data set contained a known number of
identified prey items. For analysis, we treated
each prey item as an observation and each data
set as a dietary sample. Following this logic, the
number of observations in a sample (i.e., sample
size) corresponds to the total number of prey
items identified in each data set. We justified the
use of prey items as an observational unit instead
of pellets because a pellet is difficult to define
(i.e., broken pellets are often collected or multiple
pellets are stored together and break apart
during storage) and a single pellet may contain
multiple prey items. Being an uncertain and
inconsistent measure of sample size, no pellet
total is given here.
The methods used to identify remains and
tally prey numbers followed Forsman et al.
(1984). Samples abbreviated as CAPRF2,
Volume II/Chapter 5
2
Mexican Spotted Owl Recovery Plan
ZION2, CANYL, BAR-M, MOGAZ2,
COCODM, GILADM, and SACMT2 (see
Tables 5.1-5.6 for acronym definition) were
analyzed using standardized procedures described
and implemented by DeRosier and Ward
(1994) to facilitate comparison. According to
both sources, remains were keyed to species
when possible using skulls and appendicular
skeletal parts. Specialists were consulted to
identify less common or unusual remains,
particularly bats, birds, reptiles, and invertebrates.
Deviations from our standard identification
procedures were necessary for the SCCOL
sample where invertebrate parts were not identified
(Charles Johnson, Rocky Mountain Research
Station, Fort Collins, CO, pers. comm.),
and in the ZION1 sample where appendicular
parts were not used to tally prey (Sarah
Rinkevich, FWS, Albuquerque, NM, pers.
comm.).
Owl diets were quantified using relative
frequency and percent biomass for 11 prey
groups: woodrats, white-footed (peromyscid)
mice, voles, pocket gophers, rabbits, bats, other
or unidentified small mammals (mostly murids),
other or unidentified medium mammals (mostly
sciurids), birds, reptiles, and arthropods (Tables
5.1-5.6). We use the term peromyscid mice here
in place of white-footed mice to represent the
approximate 15 North American species of the
genus Peromyscus. Confusion sometimes follows
discussion of white-footed mice because this is
also the common name for P. leucopus.
Several sources were used to estimate prey
mass (Appendix 5a). Biomass estimates given by
the original authors were retained unless better
estimates were available. Estimates of prey mass
from areas nearest to where pellets were collected
were used whenever possible. In the absence of
better data, general references for mass were
used. Averages, weighted according to proportions
of species in owl diets, were used to estimate
biomass for less specific taxa such as
“woodrat species” or “unidentified bat.”

3
Table Table 5.1. 5.1. Relative frequency of prey items found in the diet of Mexican spotted owls occurring in the northern portion of the subspecies' range. Values
were calculated from totals pooled across owl territories and years.

4
Table Table 5.2. 5.2. Relative frequency of prey items found in the diet of Mexican spotted owls occurring in the central portion of the subspecies' range. Values
were calculated from totals across owl territories and years.

5
Table Table 5.3. 5.3. Relative frequency of prey items found in the diet of Mexican spotted owls occurring in the southern portion of the subspecies' range. Values
were calculated from totals pooled across owl territories and years.

6
Table Table 5.4. 5.4. Percent of prey biomass in the diet of Mexican spotted owls occurring in the northern portion of the subspecies' range. Values were calculated
from totals pooled across owl territories and years.

7
Table Table 5.5. 5.5. Percent of prey biomass in the diet of Mexican spotted owls occurring in the central portion of the subspecies' range. Values were calculated
from totals pooled across owl territories and years.

8
Table Table 5.6. 5.6. Percent of prey biomass in the diet of Mexican spotted owls occurring in the southern portion of the subspecies' range. Values were calculated
from totals pooled across owl territories and years.

GENERAL GENERAL GENERAL FOOD FOOD HABITS
HABITS
The Mexican spotted owl eats a variety of
animals throughout its range but usually takes
small and medium-sized mammals (Table 5.7).
As a group, mammals are taken more frequently
(x = 82.1%; cv = 13.3%; n = 25 data sets) than
birds (x = 4.8%; cv = 78.4%; n = 25), reptiles
(x = 0.5%; cv = 192.5%; n = 25) or arthropods
(x = 12.6%; cv = 79.0%, n = 23). Arthropods
could be present in the owl’s diet because these
items were eaten by the owl’s prey prior to
capture. Mammal use is even greater when
biomass is considered (x = 95.8%, x = 3.9% for
birds, x = 0.1% for reptiles, and x = 0.2% for
arthropods). A cumulative plot of diet frequencies
(Figure 5.1a) indicates that 90% of an
“average” Mexican spotted owl diet would
contain 30% woodrats; 28% peromyscid mice;
13% arthropods; 9% microtine voles; 5% birds;
and 4% medium-sized rodents, mostly diurnal
sciurids. A cumulative plot of diet biomass
(Figure 5.1b) indicates that, on average, 90% of
a Mexican spotted owl diet is comprised of 53%
woodrats; 13% rabbits; 9% peromyscid mice;
9% birds; and 6% medium-sized mammals such
as diurnal sciurids. These rangewide patterns,
however, are not consistent among RUs.
To evaluate geographic variation of Mexican
spotted owl food habits, we examined diet data
by recovery unit. Frequencies of prey were
treated as binomial, either the prey species being
compared was consumed during a successful
foraging event or some other species was consumed.
We transformed these data for parametric
analyses using an arcsine-squareroot transformation
(Freeman and Tukey 1950) and tested
the hypothesis of no difference in diets among
RUs using a one-way analysis of variance
(ANOVA). A Tukey’s test was used to conduct
multiple comparisons among RUs when the
ANOVA was significant. We conducted the tests
for each of the 11 prey groups separately. We did
not conduct an ANOVA on percent biomass
estimates because these data were comprised of
both frequency and prey mass, and our estimates
of mass for prey were not significantly different
among RUs except for voles (F = 4.4, d.f. = 6,
15, P = 0.009). Thus, prey mass would have
Volume II/Chapter 5
9
Mexican Spotted Owl Recovery Plan
been roughly equivalent among RUs and comparisons
of percent biomass would have been
equivalent to those of relative frequency.
Our analyses indicated significant differences
in Mexican spotted owl diets among geographic
location (Figure 5.2). Woodrats were taken more
often in the Colorado Plateau compared to the
Upper Gila Mountains and Sierra Madre
Occidentalis - Norte (F = 4.6, d.f. = 6, 18,
P = 0.005; Figure 5.2a). Voles were consumed
more frequently by owls in the Basin and
Range - East, Southern Rocky Mountains -
Colorado, and Upper Gila Mountains RUs than
in the Colorado Plateau and Basin and
Range - West RUs (F = 8.3, d.f. = 6, 18,
P < 0.001; Figure 5.2a). Pocket gophers were
eaten more often in the Upper Gila Mountains
compared to the Colorado Plateau (F = 4.5,
d.f. = 6, 18, P = 0.006; Figure 5.2c); and birds
were consumed more often by owls in the
Southern Rocky Mountains - New Mexico,
Basin and Range - West, and Upper Gila Mountains
RUs than in the Colorado Plateau (F = 5.8,
d.f. = 6, 18, P = 0.002; Figure 5.2d). Bats and
reptiles were consumed more frequently in the
Basin and Range - West RU compared to the
Upper Gila Mountains RU (F = 2.9, d.f. = 6, 18,
P = 0.038; Figure 5.2e and F = 3.3, d.f. = 6, 18,
P = 0.024; Figure 5.2f, respectively). Of the five
groups that did not differ significantly among
RUs (peromyscid mice, rabbits, other small
mammals, other medium mammals, and
arthropods), only peromyscid mice (x = 27.2%,
cv = 42% among units) and arthropods (x =
13.8%, cv = 70%) were frequent food items.
Interregional trends in prey consumption
could be attributed to other factors like temporal
variation in the owl’s diet within each study area,
or because the breeding status of owls differed
among studies. Diet frequencies from each study
were pooled across years and owl pairs regardless
of reproductive status because this information
was unavailable in most cases. However, the year
in which diet samples were collected and the
reproductive success of a sufficient number of
owls were known for three studies (SACMT2,
GILADM, COCODM). These three data sets
were collected from two of the RUs, Basin and
Range - East (SACMT2; Tables 5.3 and 5.6) and
Upper Gila Mountains (GILADM, COCODM;

Volume II/Chapter 5
Mexican Spotted Owl Recovery Plan
Table Table 5.7. 5.7. Animal species consumed by Mexican spotted owls as determined from examination of
25 data sets collected from 18 geographic areas.
FPO
10

Volume II/Chapter 5
Mexican Spotted Owl Recovery Plan
Figure Figure Figure 5.1. 5.1. 5.1. Cumulative distributions of prey in the diet of Mexican spotted owls presented as (a) (a)
(a)
relative frequency (%) of items and (b) (b) percent biomass. Values are averages across 25 data sets conducted
throughout the owl's range and dashed lines are 95% confidence limits. Prey groups are
WRAT-woodrats; MICE-peromyscid mice; ARTH-arthropods; VOLE-voles; BIRD-birds; OMMMother
medium-sized mammals; BATS-bats; OSMM-other small-sized mammals; RABB-rabbits;
GOPH-gophers; REPT-reptiles.
11

Volume II/Chapter 5
Mexican Spotted Owl Recovery Plan
Figure Figure 5.2. 5.2. Geographic variability in the food habits of Mexican spotted owls presented as relative
frequencies of (a) (a) woodrats, (b) (b) voles, (c) (c) gophers, (d) (d) birds, (e) (e) bats, and (f) (f) reptiles. Point values are
from single studies or averages among the number of data sets shown in parenthesis. Vertical bars are
95% confidence intervals showing sampling and inter-data set variation within a recovery unit. Recovery
Unit acronyms are COPLAT-Colorado Plateau; SRM-CO-Southern Rocky Mountains - Colorado;
SRM-NM-Southern Rocky Mountains - New Mexico; UPGIL-Upper Gila Mountains; BAR-W-
Basin and Range - West; BAR-E-Basin and Range - East; and SMO-N-Sierra Madre Occidental -
Norte.
12

Tables 5.2 and 5.5). Owl reproductive success
was determined similarly in all three studies
using methods described by Forsman (1983). We
used data from these studies to evaluate the
influence of geography, time, and owl reproductive
status on the interregional trends in the owl’s
diet.
To quantify the effect of these three factors,
we analyzed the differences in relative frequency
of a given prey group in the owl’s diet among
study area (SACMT2, COCODM, or
GILADM; geographic variation), year (1991-
1993; temporal variation), and number of owl
young produced (0, 1, 2, or 3; variation in owl
reproductive status) using a three-factor
ANOVA. Prey groups that were common to
owls in any of the three study areas were analyzed
separately (woodrats, peromyscid mice,
voles, pocket gophers, rabbits, other mediumsized
mammals, and arthropods). We define
common prey arbitrarily as those species contributing
>10% of diet frequency or biomass, which
includes the majority of species identified in the
90% cumulative averages (Figure 5.1). Statistical
significance of each factor was used to quantify
the importance of these factors in determining
regional diet trends.
In 3 of 7 tests, consumption of common
prey varied primarily by geographic location
(Table 5.8). In the other 4 tests, consumption of
woodrats, peromyscid mice, medium-sized
mammals, and arthropods was influenced by an
interaction between geographic location and
year. However, significance values indicated that
the consumption of woodrats and arthropods
was influenced more by the owls’ location than
the particular year (Table 5.8). Prevalence of
geographic variation in the three-factor ANOVA
results supports our claims that the owl’s feeding
habitats differ among regions, as discussed above
(Figure 5.2).
Diet differences of the Mexican spotted owl
likely result from a combination of habitat
differences among RUs for both the owl and its
prey (See Zoogeography and Macrohabitats of
Common Prey). Landscape approaches to
management that maintain conditions for
common prey of any predator are assumed to
have beneficial effects (Reynolds et al. 1992).
However, the reliability of such conservation
Volume II/Chapter 5
13
Mexican Spotted Owl Recovery Plan
strategies must be firmly based on ecological
links among prey, predator, and environmental
conditions. Thus, it is crucial to consider relationships
among prey abundance and persistence
of owl populations, and among prey abundance,
availability, and habitat conditions.
RELATIVE RELATIVE IMPORTANCE
IMPORTANCE
OF OF PREY
PREY
Prey that positively influences owl survival,
reproduction, or numbers may increase the
likelihood of persistence of Mexican spotted owl
populations. Although no information is available
to quantify effects of food on spotted owl
survival and density, previous studies have
examined correlates between this owl’s diet and
reproduction. For example, Barrows (1987)
suggested that larger prey (e.g., woodrats) was
taken in greater frequency by owls with young.
Thrailkill and Bias (1989) reported a similar
pattern for California spotted owls occurring in
the central Sierra Nevada. In contrast, Ward
(1990) observed a different pattern for northern
spotted owls in northwestern California. He
found that large prey was taken in relatively
equal frequency by breeding and nonbreeding
owls, presumably because woodrats were a
common food resource for owls regardless of
breeding status. These different results may
reflect variation in prey availability, sampling
bias and variation, temporal variation, or true
regional differences in owl diets.
To evaluate if any particular prey group
could increase persistence of the Mexican
spotted owl, we analyzed owl reproductive
success (average number of young fledged) as a
function of diet, year, and geographic location
using a three-factor ANOVA. This approach
would allow us to quantify variation in owl
reproduction that could be attributed to the
frequency of a particular prey in the owl’s diet.
Owl reproduction related to consumption
frequency of a given prey group would imply a
relative importance of that prey. In using this
approach, we further assumed that prey species
that were positively related to reproduction also
enhanced the owl’s survival.

14
Table Table 5.8. 5.8. Factors influencing trends observed in Mexican spotted owl diets. Data are from three studies conducted in northern Arizona, the Sacramento
Mountains, New Mexico, and the Tularosa Mountains, New Mexico, during breeding seasons of 1991, 1992, and 1993.
FPO

15
Table Table 5.8. 5.8. (continued)
FPO

This analysis was conducted by stratifying
and comparing variation in the number of
young owls produced among three study areas
(SACMT2, COCODM, GILADM), three
different breeding seasons (1991-1993), and
three amounts of prey consumption, low
(< 33%), high (³ 66%), or medium. Seven prey
groups were examined in separate ANOVAs to
ensure independence among diet frequencies.
These included woodrats, peromyscid mice,
voles, gophers, rabbits, other medium-sized
mammals, and arthropods. Study area and year
were included as blocking factors to account for
spatial and temporal effects that might alternatively
explain patterns in the owl’s reproduction,
respectively. This analysis differed from the 3factor
ANOVA used to examine geographic
variation in the owl’s diet where number of
young was treated as a predictor variable rather
than a response.
Results from each ANOVA suggested that
the owl’s reproductive success was not influenced
by a single prey species but rather by many
species in combination. None of the specific
prey groups significantly influenced owl reproductive
success when diet frequencies were
examined separately (Table 5.9). Time was a
significant factor influencing the owl’s reproduction
(Table 5.9) when consumption of woodrats
or voles was examined. Prey abundance is known
to fluctuate through time. Thus, effects attributed
to temporal variation may also represent
associated changes in prey populations. However,
it is more likely that the owl’s reproductive
success was influenced by total prey biomass
consumed in a given year, rather than by a single
prey species. For example, when frequencies of
the three most common prey groups, woodrats,
peromyscid mice and voles were combined and
analyzed, diet was a nearly significant predictor
of the owl’s reproductive success (F = 2.930,
d.f. = 2, 98, P = 0.058). More owl young were
produced when moderate to high amounts of
these common prey were consumed in all three
study areas (Figure 5.3).
Contrary to the above results, certain prey
species may be more important in certain
regions of the owl’s range. For example, other
information from Ward et al. (unpublished)
suggests that reproductive success of Mexican
Volume II/Chapter 5
16
spotted owls in the Sacramento Mountains may
increase when deer mice populations irrupt. In
1991, deer mouse biomass averaged 0.911 kg/ha
in mixed-conifer forests (Figure 5.4a) and the
number of young produced corresponded to the
number of peromyscid mice consumed (Figure
5.4b). In 1992 and 1993, owl reproductive
success decreased corresponding with a reduction
in deer mouse abundance and the frequency of
peromyscid mice consumed by owls (Figure
5.4c). Reproduction among owls dwelling in
steep-walled canyons of the Colorado Plateau
may also depend on a specialized diet because
these owls consume a greater number of
woodrats compared to other localities (Table
5.1). These results may be exceptions, as most of
our findings support maintenance of several
common prey species, rather than enhancing
populations of a few.
ZOOGEOGRAPHY ZOOGEOGRAPHY AND
AND
MACROHABITATS
MACROHABITATS
OF OF COMMON COMMON PREY
PREY
As detailed earlier, Mexican spotted owls use
a variety of prey. Species regarded as “common”
are those comprising ³10% of the owl diet by
relative frequency or biomass within a given RU.
Prey commonly consumed by the owl varies
geographically (Table 5.10). This geographic
variation can be attributed to two primary
factors: the geographic range of the prey and the
degree of sympatry in macrohabitats of the owl
and its prey. Below, we provide an overview of
basic macrohabitat associations of common owl
prey.
Bats Bats
Bats
Mexican Spotted Owl Recovery Plan
MAMMALS
MAMMALS
As a group, bats are common prey in portions
of the Colorado Plateau, Upper Gila
Mountains, and Basin and Range - West RUs
and they are consumed occasionally by owls in
all RUs. If taken from outside roosts or nursery
colonies, bats may represent a low-cost, opportunistic
food source for the owls. No particular
species appears to be used in great abundance;
but when considered as a group, the importance

17
Table Table 5.9. 5.9. Factors influencing production of Mexican spotted owls in northern Arizona, the Sacramento Mountains, New Mexico, and the Tularosa
Mountains, New Mexico, during 1991, 1992, and 1993. Consumption of common prey was categorized according to the frequency of that prey in the
owls' diet; low ( 0.05) in tests on
peromyscid mice or could not be quantified in tests with other prey because of limited sample sizes.
FPO

18
Table Table 5.9. 5.9. (continued)
FPO

Figure Figure 5.3. 5.3. Reproductive success (mean number of young produced) as a function of low (

Figure Figure 5.4. 5.4. Biomass (kg/ha) of (a) (a) common prey occurring in mixed-conifer forests, (b) (b) frequencies
of peromyscid mice consumed by Mexican spotted owls stratified by number of owl young produced,
and (c) (c) average (±95% CI) number of owl young produced in the Sacramento Mountains, New
Mexico (Ward et al. unpublished). Bars in (b) (b) represent variation among owl pairs (standard errors).
Volume II/Chapter 5
20
Mexican Spotted Owl Recovery Plan

21
Table Table Table 5.10. 5.10. 5.10. Prey comprising ³10% of relative frequency (X) or biomass (O) in the diet of Mexican spotted owls.
FPO

occur within woodlands and forests. Botta’s
pocket gopher, northern pocket gopher, and
southern pocket gopher occur within the range
of the Mexican spotted owl. Botta’s pocket
gopher is the most widespread, being found in
most vegetation types. The northern pocket
gopher occurs in montane habitats of the northern
part of the owls’ range. The southern pocket
gopher is found in Basin and Range - West and
Mexican RUs. Both Hoffmeister (1986) and
Findley et al. (1975) noted that Botta’s pocket
gopher is ubiquitous whenever soil is suitable for
burrowing, whereas the northern pocket gopher
is more typically found in parks and meadows
within montane forests. Findley et al. (1975)
stated that the southern pocket gopher inhabits
shallow, rocky soils of pine forests.
Peromyscid Peromyscid Mice Mice
Mice
Eight peromyscid mice occur within the
range of the Mexican spotted owl. Only two
species, the deer mouse and brush mouse are
consumed regularly by owls in all RUs (Table
5.10). A third species, the canyon mouse, is
likely consumed by owls dwelling in the Colorado
Plateau RU and the rock mouse has been
reported in the diet of owls occurring in the
Basin and Range - East RU (Table 5.7).
The deer mouse is widespread, inhabiting all
vegetation types except high-elevation tundra
(Bailey 1931, Hall and Kelson 1959, Armstrong
1977, Goodwin and Hungerford 1979). High
reproductive success of spotted owls in the
Sacramento Mountains, New Mexico, (Basin
and Range - East RU) has been recorded during
irruptions of deer mice in mixed-conifer forests
(See Abundance and Distribution of Common
Prey, Sacramento Mountains).
More restricted in distribution, the brush
mouse typically inhabits areas with extensive
rock and shrub cover in pinyon-juniper, riparian,
oak, and pine-oak woodlands (Wilson 1968,
Armstrong 1979, Svoboda et al. 1988).
Goodwin and Hungerford (1979) found that
brush mice inhabit rocky slopes in central
Arizona’s pine-oak forests, but rarely use pure
stands of pine.
The canyon mouse occupies the canyon
walls, cliffs, and steep rocky slopes of northern
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22
Mexican Spotted Owl Recovery Plan
Arizona, Utah, northwestern New Mexico, and
western Colorado (Armstrong 1979, Johnson
and Armstrong 1987). Findley et al. (1975)
reported that the canyon mouse is often found
in pinyon-juniper woodlands at the base of cliffs,
although Johnson and Armstrong (1987) noted
that vegetation associations are of limited importance
relative to the presence of suitable rocky
substrates.
The rock mouse is found in association with
rocky substrates generally above 1,900 m (6,230
ft) elevation (Findley et al. 1975, Cornely et al.
1981). This species occurs in most of the United
States portion of the owl’s range and is often
sympatric with deer mice and brush mice (Wilson
1968, Cornely et al. 1981, Ribble and
Samson 1987).
Woodrats Woodrats
Woodrats
Mexican, bushy-tailed, desert, and whitethroated
woodrats are consumed by Mexican
spotted owls. For the owl, woodrats provide a
large mass of food per capture. This prey is a
primary food source for owls through most of its
range but particularly in the canyon habitats of
the Colorado Plateau RU, where all four species
of woodrats are sometimes found (Table 5.10).
The Mexican woodrat is perhaps the most
common woodrat found within the range of the
Mexican spotted owl. It occurs within all RUs,
although populations are disjunct because of the
species’ montane distribution (Cornely and
Baker 1986). The altitudinal range of the Mexican
woodrat begins in the lower pine zone and
extends upward through mixed-conifer forests
where Findley et al. (1975) reported they reach
their greatest abundance. Hoffmeister (1986; see
also Goodwin and Hungerford 1979) regarded
Mexican woodrats as rock dwellers within these
vegetation types, infrequently extending into
pinyon-juniper woodlands. Armstrong (1972),
however, reported that this species typically uses
pinyon-juniper woodland in western Colorado
and scrub-like oaks and mountain mahogany
vegetation along the eastern foothills northwards
almost to Wyoming. The range of Mexican
woodrats in Utah is restricted to the southeastern
portion of the state, east of the Colorado River.

Presumably, the species uses similar habitats in
Utah as it does in western Colorado.
Bushy-tailed woodrats are a common diet
component within the Colorado Plateau and
both Southern Rocky Mountain RUs. This
species is a cordilleran mammal of western
Colorado, northcentral and northwestern New
Mexico, northeastern Arizona, and eastern Utah
(Durrant 1952, Hoffmeister 1986, Findley et al.
1975, Armstrong 1972, 1979). Finley (1958)
reported that bushy-tailed woodrats use a variety
of vegetation types, primarily woodland and
shrublands. Their distribution may depend on
the presence of suitable rock outcrops rather
than specific vegetation (Finley 1958,
Hoffmeister 1986). At higher elevations, these
outcrops interrupt open forests of Douglas-fir,
aspen, or ponderosa pine containing a welldeveloped
shrub understory. Typically, lower
elevation sites are dominated by pinyon and
juniper.
The desert woodrat is consumed by owls in
the Colorado Plateau RU. This species is most
abundant in the Arizona strip where it inhabits a
variety of plant communities including creosote
bush and cacti to junipers and pine (Hoffmeister
1986). Desert woodrats frequently nest in
crevices of cliffs and rock outcrops within
juniper or shadscale plant communities of Utah
and Colorado, below 2,000 m (6,560 ft) elevation
(Finley 1958).
White-throated woodrats are common prey
of owls occurring in the Upper Gila Mountains
and Basin and Range - West RUs and are less
frequently consumed by owls in other RUs. This
woodrat species is typically distributed below the
conifer belt, although it can be found in pinyonjuniper
woodlands (Hoffmeister 1986).
Voles
Voles
Four species of voles are common prey of the
Mexican spotted owl including the Mexican (or
Mogollon vole [after Frey and LaRue 1993]),
mountain, meadow, and long-tailed voles (Table
5.10). Three of these species can be ordered
along an environmental moisture gradient from
semi-arid (Mexican vole), mesic (mountain
vole), to hydric (meadow vole). Long-tailed voles
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23
Mexican Spotted Owl Recovery Plan
inhabit environments along the entire gradient
(Getz 1985).
The Mexican vole is common within the
greatest number of RUs, including Basin and
Range - East, Southern Rocky Mountains - New
Mexico, and Upper Gila Mountains RUs. It is
fairly widely distributed in Arizona and New
Mexico, but it is confined to the southeast part
of Utah and to southwest Colorado. This
species occurs in the widest range of habitats of
any microtine and is generally associated with
xeric grassy locations extending from pinyonjuniper
to spruce-fir zones (Armstrong 1972,
Findley and Jones 1962, Findley et al. 1975,
Finley et al. 1986, Hoffmeister 1986, Frey and
LaRue 1993).
The two species associated with wet conditions
(mountain and meadow voles) generally
occur in the northern portion of the owl’s range.
Mountain voles are common prey in the Colorado
Plateau and both Southern Rocky Mountain
RUs. In these areas, the mountain vole
occupies forest meadows ranging in elevation
from open pine-oak to spruce-fir forests.
Armstrong (1977) found mountain voles in
dense grass cover with a sparse overstory. This
vole’s geographic range includes most montane
regions along the north-south axes of Colorado
and Utah, northern New Mexico, and the White
Mountains in Arizona. Meadow voles occur in
both Southern Rocky Mountains RUs where
permanent water is provided by springs and
marshes (Armstrong 1972, Findley et al. 1975,
Finley et al. 1986).
The long-tailed vole occurs within the
Southern Rocky Mountains - New Mexico,
Upper Gila Mountains, and Basin and Range -
East RUs. Findley et al. (1975) reported that it is
associated with meadows and forest edge, being
most common in the mixed-conifer and sprucefir
zones but also using mixed-conifer stringers
found along canyons in the ponderosa pine
zone. Armstrong (1972, 1977) noted that this
microtine requires a grassy understory less than
other vole species because it is often found
within forests supporting minimal grass cover.

Birds
Birds
Birds are common prey for the owls in the
Southern Rocky Mountains - New Mexico,
Upper Gila Mountains, and Basin and
Range - West RUs where numerous species have
been identified in pellets (Table 5.7). The
importance of birds to spotted owls is uncertain.
Birds do contribute to the diversity of prey taken
by owls and may provide food resources when
small mammals are less abundant. However, use
of birds as prey is likely seasonal because many of
the passerine species consumed by owls are
migratory. All species identified in the owls’ diet
to date are forest dwellers.
Arthropods
Arthropods
Arthropods are common prey of spotted
owls in the Colorado Plateau, Southern Rocky
Mountains - Colorado, Southern Rocky Mountains
- New Mexico, and Upper Gila Mountains
RUs. Many species are consumed (Table 5.7).
The importance of arthropods to spotted owls is
also uncertain. If one considers biomass alone,
arthropods contribute little to the owl’s diet.
However, arthropods may provide a low cost,
high quality food taken opportunistically.
Description of macrohabitats of arthropods
consumed by spotted owls is beyond the scope
of this document. Active management of arthropod
populations for owl recovery is probably not
necessary.
Volume II/Chapter 5
ABUNDANCE ABUNDANCE ABUNDANCE AND AND
AND
DISTRIBUTION DISTRIBUTION OF OF
OF
COMMON COMMON PREY
PREY
The availability of prey to Mexican spotted
owls depends on prey abundance, the vulnerability
of the prey to capture by the owl, and the
probability that the owl and its prey occur in the
same habitat. All of these factors vary by habitat
condition. In addition, the amount of energy
available to the owl will vary according to the
type, size, and condition of the prey. Thus, it is
useful to convert prey numbers into values that
reflect energy input. Because rodents are the
most common prey of the spotted owl, we
24
Mexican Spotted Owl Recovery Plan
assume that most of the difference in energy
content among mammalian prey can be attributed
to body mass.
Although no information exists on the
vulnerability of different prey species to capture
by Mexican spotted owls, estimates of common
prey abundance and mass within several different
vegetation communities are available from
research conducted in northern Arizona (Block
and Ganey, unpublished) and the Sacramento
Mountains, New Mexico (Ward et al., unpublished).
These two studies provide estimates of
biomass and microhabitat associations (See Prey
Habitat) for the owl’s common prey in four
different vegetation communities used by owls
for foraging, ponderosa pine-Gambel oak,
mixed-conifer, high-elevation meadows, and
ponderosa pine-pinyon-juniper woodlands. The
methods and results of both studies are briefly
described below.
Northern Northern Arizona
Arizona
Methods
Methods
Small mammal populations were sampled
using live-trapping and mark-recapture techniques
from November 1990 through December
1992 within home ranges of five owl pairs. The
purpose of the sampling was to estimate biomass
of the owl’s common prey and determine the
prey’s distribution. Common prey were determined
from owl pellets collected during this
study.
The study area consisted of ponderosa pine-
Gambel oak forest, although each trapping grid
was unique with respect to the relative composition
and structure of the vegetation. Ancillary
trapping was conducted within the winter range
of two owls that migrated downward to pinyonjuniper
woodland in the Verde Valley. This
trapping was confined to five sets of smaller
trapping grids (described below) for a total of
574 trap nights.
Trapping grids were randomly established at
general foraging areas identified by radio telemetry
(Ganey and Block, unpublished data). Traps
were arrayed in 10 x 10 or 2 x 10 grids with
20-m (65.5 ft) spacings between stations. The

larger grids were used to estimate both density
and habitat correlates; the smaller grids were
used only to assess habitat use by species (see
Prey Habitat). Large Sherman live traps (size
8 x 9 x 23 cm [3 x 3.5 x 9 in]) were placed at
each grid station; extra-large Sherman live traps
(size 10 x 18 x 60 cm (4 x 4.5 x 15 in) were
placed at alternate stations. Two sizes of traps
were used to minimize the potential bias against
capturing larger prey such as woodrats in the
smaller traps.
Grids were trapped from 3-7 nights during
each trapping session. Traps were left open
during the day to sample diurnal sciurids. The
goal was to continue trapping until 90% of all
captures were recaptures to approach assumptions
of population closure. This goal was
typically reached between five and seven nights.
During periods of inclement weather, however,
we relaxed this goal to minimize trapping
mortalities. Each grid was trapped for 5-7
sessions during the study. Total trapping effort
was 49,911 trapnights (adjusted for closed and
unoccupied, or otherwise unavailable traps).
When an animal was captured, it was identified
to species, weighed, and marked by toe clipping.
Abundance was estimated as the number of
individuals per effective sampling area (ha) using
closed population estimators (Program CAP-
TURE; Otis et al. 1978, White et al. 1982).
Although the number of individuals captured at
some grids during some seasons was insufficient
for producing unbiased estimates, we considered
the closed population estimators in Program
CAPTURE more appropriate than minimum
numbers alive per grid area. The former permitted
estimating capture probabilities and sampling
variances plus population size; the latter
would not.
Biomass of common prey, expressed as
kilograms per hectare (kg/ha), was calculated as a
product of prey density and average mass. The
delta method (Goodman 1960) was used to
estimate the sampling variance of biomass from
the variances associated with sampling prey
density and mass.
Volume II/Chapter 5
25
General General Distribution Distribution
Distribution
Mexican Spotted Owl Recovery Plan
The three primary prey species captured in
ponderosa pine-Gambel oak forests were deer
mouse, brush mouse, and Mexican woodrat.
Other prey species captured included pinyon
mouse, white-throated woodrat, Stephens’
woodrat, Mexican vole, rock squirrel, graycollared
chipmunk, and cliff chipmunk. Brush
mice and white-throated woodrats were captured
with the greatest relative frequency in pinyonjuniper
woodlands. The trapping efforts did not
sample prey species such as pocket gophers,
cottontail rabbits, birds, and arthropods. Further,
only the three primary species were captured
in sufficient numbers to permit density
calculations or estimates of habitat correlates.
Thus, our analyses of population size and habitat
use address only these three species.
Population Population Abundance
Abundance
The deer mouse was the most abundant
species captured, followed by the brush mouse
and Mexican woodrat. A seasonal trend of
decreased prey biomass during winter was noted
(Figure 5.5a). Prey abundance and biomass also
varied by year (Figure 5.5a) and among owl
territories (Block and Ganey, unpublished data).
Sacramento Sacramento Mountains
Mountains
Methods
Methods
The Sacramento Mountains are located in
southcentral New Mexico. An investigation of
the abundance and distribution of common
mammalian prey began in 1991 and is ongoing
(Ward et al., unpublished data). Common prey
were determined from owl pellets collected
during this study. Abundance was estimated
among three general vegetation communities
using mark-recapture methodology.
The three communities included mesic
forests, xeric forests, and meadows. Mesic forests
were a mixture of Douglas-fir, white fir, southwestern
white pine, ponderosa pine, and
Englemann spruce (i.e., mixed conifer). Meadows
consisted of forbs and grasses and were

Volume II/Chapter 5
Mexican Spotted Owl Recovery Plan
Figure Figure Figure 5.5. 5.5. Average biomass of common prey (kg/ha) of the Mexican spotted owl in (a) (a) pine-
Gambel oak habitats of northern Arizona (Block and Ganey unpublished data) and (b) (b) in three habitats
of the Sacramento Mountains, New Mexico. Vertical bars are standard errors. Lower horizontal
bars in (b) (b) (b) separate sampling error from errors associated with variation among sites. Number of sites
within each habitat are shown in parenthesis.
26

associated with drainage bottoms adjacent to
mesic forests. Xeric forests included ponderosa
pine, pinyon, juniper, and low-growing oaks.
The same two sizes of live-traps described for
the northern Arizona study were used to capture
prey in the Sacramento Mountains. Traps were
also arranged similarly, with the following
exceptions. In 1991, four 13-ha (32.1-ac)
trapping grids were established as part of a pilot
study. Two grids were placed in the mesic forest
and two in the xeric forest. In 1992 and subsequent
years, six 4-ha (9.9-ac) trapping grids were
placed in each of the mesic and xeric forest
types. Traps were arrayed as 11 x 11 station grids.
In addition, six 1.8-ha (4.5-ac) grids were
established in meadows. Each of the latter grids
consisted of 105 large Sherman traps spaced
15 m (49.2 ft) apart in a 5 x 21 array.
All grid sites were selected randomly from a
list of known Mexican spotted owl territories.
Grids were placed as close to a nest or roost area
as possible while maintaining homogeneity at a
scale analogous to a forest stand. In addition,
each grid was £ 0.8 km (0.5 mi) from a nest or
roost to ensure that the site was available for use
by spotted owls.
All captured individuals were marked with
uniquely numbered ear tags in both ears. Loss of
both tags during an eight-night trapping session
was less than 1% for all marked species. All other
methods of sampling and data collection were
similar to the study in northern Arizona (Block
and Ganey, unpublished data). We therefore
considered the results of both studies to be
comparable. Prey abundance and biomass were
estimated using the same procedures described
for the northern Arizona study. Tests for spatial
and temporal differences in prey biomass were
conducted using a two-factor ANOVA.
General General Distribution
Distribution
Common prey included woodrats,
peromyscid mice, voles, arthropods, cottontail
rabbits, and other medium-sized mammals such
as long-tailed weasels, red squirrels, and chipmunks
(Tables 5.3 and 5.6). Cottontails and
other medium-sized mammals were consumed
infrequently but larger estimates of mass from a
few individuals resulted in larger biomass calcu-
Volume II/Chapter 5
27
Mexican Spotted Owl Recovery Plan
lations from these prey groups. However, the
exact sizes of consumed individuals were undetermined
and the range of mass for larger prey
consumed by owls could have been considerable.
For example, the size of a cottontail taken by a
spotted owl could range 50 to 400 g (1.8-14.1
oz) whereas a peromyscid mouse could range 10
to 40 g (0.4 to 1.4 oz). This potentially results in
upwardly biased estimates of biomass for larger
species in the owls’ diet. For this reason, we are
uncertain about the role of cottontails and other
medium-sized prey as common food resources
for the owl. In contrast, arthropods comprised
11.4% of the diet but were not considered
energetically important because of their small
mass (1-2 g [0.04-0.07 oz]).
Five species common in the owl’s diet were
captured regularly during live-trapping. The
distribution of each species varied by vegetation
community. Deer mice were found in all three
communities. Brush mice were restricted to the
xeric forest type and were primarily associated
with areas containing shrub-form oaks. Longtailed
voles and Mexican voles were more common
in meadows, but they also occupied the
transition zones between meadows and mesic
forests. Mexican voles were also found infrequently
in xeric forests. Mexican woodrats
occupied mesic forests and the ecotone between
these forests and meadows, as well as xeric
forests. Medium-sized mammals such as the
gray-footed chipmunk were found in mesic
forests, the edges between mesic forests and
meadows, and rarely in xeric forests. Cottontail
rabbits and red squirrels were only encountered
in mesic forests. However, our sampling procedures
were inadequate for estimating abundance
and distribution of these species and of
arthropods.
Population Population Abundance Abundance
Abundance
Total biomass (kg/ha) of five common prey
(Figure 5.5b) varied annually over the three
summers 1991-1993 (F = 12.7, d.f. = 2, 32,
P < 0.001) and also seasonally during the summer-fall-winter
period of 1993-1994 (F = 17.0,
d.f. = 2, 21, P < 0.001). Fluctuations in prey
biomass also varied by vegetation community
during both annual (F = 5.5, d.f. = 2, 32,

P = 0.009) and seasonal cycles (F = 5.8, d.f. = 2,
21, P = 0.010). The general trend was that prey
biomass was moderately high during the summer
(when owls feed their young) of 1991, peaking
in 1992, then decreasing to moderate levels in
1993 (Figure 5.5b). Further, temporal trends
differed by vegetation community. Prey biomass
decreased in mesic forests and meadows over
consecutive summers but increased then decreased
in xeric forests during this same period
(Figure 5.5b). This relationship was evident by a
statistically significant interaction of vegetation
community and year on prey biomass (F = 3.3,
d.f. = 3, 32, P = 0.032). Whereas prey biomass
pooled across all communities decreased from
the summer to fall of 1993 before increasing
slightly in the winter (Figure 5.5b), seasonal
trends differed among communities (F = 17.0,
d.f. = 2, 21, P < 0.001). These patterns also
showed an interactive influence of season and
vegetation community on prey biomass (F = 3.0,
d.f. = 2, 21, P = 0.044). Thus, abundance of
potential food resources for the Mexican spotted
owl in the Sacramento Mountains are temporally
variable and habitat dependent.
The variations in total prey biomass were
also reflected in the population dynamics of
different species (Figure 5.6a). For example, deer
mice densities within mesic forests peaked in the
summer of 1991 and declined through the
summer of 1993 while maintaining low densities
in the meadows (Figure 5.6b). Deer mice in
xeric forests maintained lower, relatively stable
densities that peaked in summer of 1992 (Figure
5.6c). In contrast, Mexican voles maintained
low, stable populations in the mesic forests but
increased dramatically in meadows and moderately
in xeric forests in the summer of 1992
before crashing in both habitats during the
summer of 1993 (Figure 5.6).
In summary, the two studies indicate that
the owl’s food resources are quite variable among
vegetation communities and through time.
Arranging the four vegetation communities
examined in these two studies in descending
amount of summer prey biomass indicates that
meadows > mixed-conifer forest > ponderosa
pine-pinyon-juniper-oak woodlands > ponderosa
pine-Gambel oak forest. When considering
other factors that influence the availability of
Volume II/Chapter 5
28
Mexican Spotted Owl Recovery Plan
prey, mixed-conifer forests likely provide the
greatest amount of food during summer periods.
Rearranging the same communities according to
winter prey biomass indicates that meadows >
ponderosa pine-pinyon-juniper-oak woodlands >
ponderosa pine-Gambel oak forest > mixedconifer
forest. Accounting for the availability of
prey, woodlands with a mixture of ponderosa
pine, pinyon-juniper, and oaks provide more
prey to owls during winter months than the
other three communities. However, temporal
peaks of prey cycles are not correlated among
these communities. That is, when prey are
abundant in mixed-conifer forest one year and
low a subsequent year, an opposite pattern may
occur in a different vegetation community. The
asynchrony of abundance among prey species,
vegetation communities, and time may provide a
buffer against the effects of extreme oscillation in
prey cycles. This implies maintaining a mixture
of vegetation communities within the owl’s
foraging range.
Results of both studies also showed that the
owl’s food is most abundant during the summer
when young are being raised. Decreases in prey
biomass occur from late-fall through winter.
Seasonal decreases, like these, are typical of small
mammal populations. Unfortunately, explanations
for fluctuations in small mammal populations
are equally variable and include artificial
random patterns in population data, weather
changes, behavioral mechanisms, predation, and
age-related effects on demographic processes
(e.g. fecundity, dispersal; see reviews by Conley
and Nichols 1978, Finerty 1980).
Although the reasons for seasonal declines in
prey and their ramifications on the owl have not
been quantified, conditions that increase winter
food resources will likely improve conditions for
the owl. For example, Hirons (1985) has shown
that large body reserves of fat and protein are
essential during incubation by female tawny owls
for successful reproduction. Abundant prey
populations during winter and early spring
periods increase the likelihood of egg laying and
decrease the rate of nest abandonment (Hirons
1985).
Obviously, there will be little recourse for
enhancing prey populations if factors like precipitation,
temperature, or amount of snow

Volume II/Chapter 5
Mexican Spotted Owl Recovery Plan
Figure Figure Figure 5.6. 5.6. Trends in average density (no./ha) of common prey of the Mexican spotted owl in (a)
(a)
mixed-conifer forest, (b) (b) montane meadows, and (c) (c) ponderosa pine-pinyon-juniper-oak woodlands,
Sacramento Mountains, New Mexico. Summer (1992-93) values are based on 6 spatial replicates;
summer (1991), fall, and winter values are based on 2 replicates.
29

cover are the major causes of decline in prey
populations. The degree to which habitat manipulation
can ameliorate against weather effects
or enhance prey availability requires investigation
and is encouraged. Successful manipulation
may provide a potent tool for recovering Mexican
spotted owls or other predators in the future.
PREY PREY HABITAT
HABITAT
Ensuring adequate food for the owl requires
conserving and possibly restoring habitat of the
owl’s prey. Ideally, to succeed, those features of
the environment that consistently cause increases
in abundance and availability of desired prey
species should be identified. In reality, few
habitat studies are so revealing or precise (see
Verner et al. 1986). However, habitat studies
often do identify patterns and descriptive correlates
of animal distribution or abundance.
Although crude, this type of information frequently
is all that is available for predicting the
outcome of planning decisions or management
prescriptions.
In the absence of cause-effect relationships
among the owl’s prey and its habitat, we present
habitat correlates for the distribution of several
common prey species. This information was
determined from the same studies of prey
abundance conducted in northern Arizona
(Block and Ganey, unpublished data) and the
Sacramento Mountains (Ward et al., unpublished
data).
Northern Northern Northern Arizona Arizona Arizona - - - Pine-oak Pine-oak Pine-oak Forest Forest
Forest
Field Field Methods Methods and and Statistical Statistical Analyses Analyses
Analyses
Habitat-sampling plots were established as a
5-m [16.5-ft) radius centered at each trapping
station (n = 1,260). Cover by grass, forbs, rock,
dead woody debris of three size classes (10 cm [3.9
in]), and live woody vegetation at four height
strata (2-5 m
[6.6-16.4 ft], >5 m [16.4 ft]) were estimated as
the percentage of 10 point intercepts (at 1-m
[3.3 ft] intervals along a randomly oriented
transect) covered by each of these variables. Tree
Volume II/Chapter 5
30
diameters were measured with a dbh tape;
heights were measured with a clinometer. Shrub
and slash pile heights were measured with a
meter stick. Mid-point diameters and lengths of
logs within the plot were measured with a
measuring tape. Numbers of trees and shrubs by
species were recorded. Slope was measured with
a clinometer and aspect with a compass.
Deer mice, brush mice, and Mexican
woodrats were captured in sufficient numbers to
permit habitat analyses. Stations where each
species was captured were contrasted with those
where it was not captured using analysis of
variance with owl territory as a blocking factor.
Two other analyses were also conducted. Logistic
regression was used to examine differences
between stations where each species was and was
not captured that may not have been identified
in the ANOVA. Stepwise multiple linear regression
(Draper and Smith 1981) was used to
evaluate relationships between small mammal
population levels and habitat characteristics. The
dependent variable was the number of trapping
stations/grid where the species was captured.
Independent variables were habitat characteristics
aggregated across the grid.
Results
Results
Mexican Spotted Owl Recovery Plan
Deer mice used more open sites, on gentler
slopes, and with less shrub and midstory canopy,
smaller densities of Gambel oak trees and shrubs,
but more slash piles and greater litter depth than
stations where it was not captured (Table 5.11).
In contrast, brush mice and Mexican woodrats
both used sites characterized by greater slopes,
low vegetation cover, sparser tree canopy (>5 m
[16.4 ft]) cover, more Gambel oak shrubs, and
greater log volume than areas where they were
not captured (Table 5.11). Further, brush mice
used areas with greater Gambel oak tree density
and basal area and less ponderosa pine basal area
than found at stations where it was not captured.
Tree basal area at sites where Mexican woodrats
were captured was significantly less and total
rock cover was significantly greater than at sites
where it was not captured.
Generally, results from logistic regression
analyses corroborated results of the univariate
analyses. Deer mice were associated with areas of

31
Table Table 5.11. 5.11. Descriptive statistics (means with SE in parentheses) of selected habitat variables characterizing habitats of common mammalian prey of
Mexican spotted owls (4 territories) in ponderosa pine-Gambel oak forests, northern Arizona, 1990-1992.

32
Table Table 5.11. 5.11. (continued)
FPO

little slope, Gambel oak, and mid-story (2-5 m
[6.6-16.4 ft]) vegetation. Brush mice and Mexican
woodrats used areas with greater shrub
density, rock cover, log volume, and Gambel oak
cover.
In the multiple regression analysis, no
variable entered the model for deer mice, suggesting
that it is a habitat generalist. Two variables,
shrub density and grass height, entered the
regression model for brush mice. These two
variables alone explained >96% of the variation
in the data set. For Mexican woodrats, shrub
density and slope entered the model and explained
>92% of the variation in numbers. Thus,
both brush mice and Mexican woodrats were
apparently more stenotypic in habitat than deer
mice and closely associated with shrub cover
provided by Gambel oak and New Mexican
locust.
Sacramento Sacramento Mountains
Mountains
Field Field Field Methods Methods and and Statistical Statistical Analyses Analyses
Analyses
Habitat characteristics were measured within
circular plots of 5-m [16.4-ft] radius centered at
about 80% of the trap stations (n = 1,416).
Stations were stratified by vegetation community:
mesic forest (n = 583), xeric forest
(n = 578), and meadow (n = 255). Within each
plot, methods similar to those described above
were used with the following exception: tree
basal area and density were estimated with a
plotless method using 10- and 20-factor prisms
rather than the plot methods used in the ponderosa
pine-Gambel oak forest of northern Arizona.
Also, cover of woody vegetation by height
strata was not recorded in the Sacramento
Mountains.
Deer mice, brush mice, Mexican woodrats,
long-tailed voles, and Mexican voles were captured
in sufficient numbers to permit habitat
analyses. Statistical analyses for each species were
done separately by vegetation community.
Habitat characteristics of trap stations where a
species was captured were contrasted with
stations where they were not captured using
Student’s t-test. A random sample of unused
stations equal to the number of used stations was
Volume II/Chapter 5
33
selected to meet the assumption of equal sample
size except for Mexican voles in meadows, which
were captured at >75% of the trap stations.
Consequently, a subset of used stations equal to
the available number of unused stations was
randomly selected (n = 62) for conducting the
analysis. Logistic regression was also used to
determine the relative value of variables in
distinguishing between stations where the
animal was and was not captured. This second
analysis was used to detect other variables that
might identify habitat correlates not identified
by use of Student t-tests.
Results
Results
Mexican Spotted Owl Recovery Plan
Mesic esic F FFor
F or orests. or ests. ests.—Microhabitat ests.
analyses were
possible for deer mice, Mexican woodrats, and
long-tailed and Mexican voles. Deer mice were
captured in areas with little herbaceous cover and
extensive exposed soil (Table 5.12). Results from
the logistic regression indicated that deer mice
used areas with less herbaceous cover and greater
densities of live conifer trees. Mexican woodrats
used areas that had greater shrub but less herbaceous
cover (Table 5.13). Shrub cover was the
only variable included in the stepwise logistic
regression model of habitat use by Mexican
woodrats. Long-tailed voles occurred in areas
characterized by less slope, less tree cover and
exposed soil but greater herbaceous cover, fewer
stumps, greater shrub numbers, and fewer
conifer snags (Table 5.14). According to the
logistic regression model, long-tailed voles used
areas with less exposed soil, greater shrub density,
and less slope. Mexican voles used sites with less
shrub, tree and exposed ground cover, greater
herbaceous cover, fewer shrubs, fewer conifer
seedlings and saplings, lower density and less
basal area of deciduous trees (Table 5.15).
Mexican voles used sites with less tree cover and
lower deciduous tree density according to the
logistic regression model.
Xeric eric eric FF
For FF
or or orests. or ests. ests.—Habitat ests. analyses were
possible for deer mice, brush mice, Mexican
woodrats, and Mexican voles. As in mesic forests,
deer mice occupying xeric forests were captured
in areas with more exposed soil than at
noncapture stations (Table 5.12). In contrast
with mesic forests, deer mice in xeric forests were

34
Table Table 5.12. 5.12. Habitat characteristics used by deer mice in three vegetation communities of the Sacramento Mountains, New Mexico. Only those variables
that differed significantly between trap stations where deer mice were and were not captured are reported.
FPO

35
Table Table 5.13. 5.13. Habitat characteristics used by Mexican woodrats in two vegetation communities of the Sacramento Mountains, New Mexico. Only those
variables that differed significantly between trap stations where woodrats were and were not captured are reported.
FPO

36
Table Table 5.14. 5.14. Habitat characteristics used by long-tailed voles in two vegetation communities of the Sacramento Mountains, New Mexico. Only those
variables that differed significantly between trap stations where long-tailed voles were and were not captured are reported.
FPO

37
Table Table 5.15. 5.15. Habitat characteristics used by Mexican voles in three vegetation communities of the Sacramento Mountains, New Mexico. Only those
variables that differed significantly between trap stations where Mexican voles were and were not captured are reported.
FPO

found on flatter areas with less rock but greater
shrub cover, and greater density and basal area of
live conifer trees (t-test, P < 0.05). Logistic
regression identified slope, density of live conifer
trees, litter depth, and number of shrub species
as useful variables for distinguishing deer mouse
habitat. Brush mice were found in areas having
less tree cover, greater rock cover, shallower litter
depth, greater densities of shrubs, gray oak, and
conifer seedlings and saplings, but fewer conifer
trees (Table 5.16). Logistic regression results
indicated that brush mice used areas with shallower
litter depth, greater shrub density, and
fewer conifer trees. Mexican woodrats were
captured in areas with greater shrub cover and
density, and greater cover by gray oak (Table
5.13). Shrub cover was the only variable that
discriminated capture from noncapture sites by
logistic regression. Mexican voles were found at
sites with greater herbaceous cover and height,
and greater density and basal area of conifer
snags (Table 5.15). Logistic regression identified
two variables, density of conifer snags and height
of herbaceous cover, as habitat discriminates for
Mexican voles occupying xeric forests.
Meado eado eadows. eado ws. ws.—Deer ws. mice, long-tailed voles,
and Mexican voles were captured frequently
enough to permit analyses. As in both forest
types, deer mice occupying meadows were
captured in areas with more exposed soil (Table
5.12). These mice also used areas with steeper
slopes, shallower litter depth, and more shrub
species (Table 5.12). Logistic regression indicated
that only steeper slopes could be used to
distinguish between capture and noncapture sites
of deer mice. Long-tailed voles were captured at
stations with less herbaceous cover, greater shrub
density, and a greater number of shrub species
(Table 5.14). Even though cover by herbaceous
vegetation was less at capture stations, it still
averaged 90.0% (SE = 2.8). Shrub density and
herbaceous cover were the two variables that
separated capture from noncapture sites using
logistic regression. Mexican voles were found on
flatter areas with greater herbaceous cover and
height, greater litter depth, and less exposed
ground (Table 5.15). Logistic regression identified
slope, height of herbaceous vegetation, and
litter depth as habitat variables associated with
the presence of Mexican voles in meadows.
Volume II/Chapter 5
38
DISTURBANCE DISTURBANCE EFFECTS EFFECTS ON
ON
OWL OWL PREY PREY AND AND HABITAT
HABITAT
The distribution and abundance of the
spotted owl’s prey are influenced by both natural
and anthropogenic factors. Though all factors to
some degree have formative character, many are
more accurately described as disturbance factors.
Definitions of disturbance and the magnitude of
associated effects vary according to ecological
scale and conditions. Here, we briefly discuss
fire, tree harvesting, and livestock grazing because
these activities operate at spatial scales
likely to influence spotted owls. Specifically, they
may determine whether an owl occupies and
reproduces in a given area. Important to this
discussion is the element of human control over
these disturbance activities.
We know little about direct cause-effect
relationships of most natural and anthropogenic
disturbance factors on owl prey populations.
Correlative information allows us to infer some
effects but most published research is from areas
outside the range of the Mexican spotted owl.
Their applicability to southwestern conditions is
uncertain. Furthermore, effects of disturbance
will vary by species, time, and space. Consequently,
it is important to view disturbance at
each of these scales. The issue becomes even
more complicated when one considers the
synergistic and cumulative effects of multiple
disturbances. The latter scenario is more likely
the norm than the exception.
Fire Fire
Fire
Mexican Spotted Owl Recovery Plan
Generalizing about the effects of fire on the
owl’s prey is impossible for a number of reasons
including variations in fire characteristics and in
prey habitat. Fire intensity, size, and behavior are
influenced by numerous factors such as vegetation
type, moisture, fuel loads, weather, season,
and topography. Data presented in the previous
sections illustrate how macrohabitat and microhabitat
associations of the owl’s prey vary both
geographically within a species and among
species.
Fire can effectively alter vegetation structure
and composition thereby affecting small mam-

39
Table Table 5.16. 5.16. Habitat characteristics used by brush mice in xeric forests of the Sacramento Mountains, New Mexico. Only those variables that differed
significantly between trap stations where brush mice were and were not captured are reported.
FPO

mal habitats. Population responses by small
mammals to fire-induced changes in their
habitat vary. For example, deer mouse populations
might increase immediately following fire
and then decrease through time (Peterson et al.
1985, Kaufman et al. 1988). Based on limited
sampling efforts restricted to one location,
Campbell et al. (1977) noted that populations of
peromyscid mice decreased immediately following
fire in an Arizona ponderosa pine forest that
removed one-fourth (moderately burned) to
two-thirds (severely burned) of the basal area;
populations then returned to prefire numbers
two years following the burn. Further, no differences
were found in rodent populations between
moderately and severely burned areas. They
concluded that the effects of the fire that they
studied were short-term, and the short-term
positive numerical responses by mice were
attributed to an increase in forage, particularly
grasses and forbs.
However, we suspect that effects of more
intense stand-replacing fires that dramatically
alter forest structure and move the system to
earlier seral stages would have longer-term effects
on rodent populations. Likely, early successional
species (such as the deer mouse) and those that
require open habitats with a well developed
herbaceous understory (such as microtine voles
and pocket gophers) would benefit. In contrast,
species that require a wooded or forested overstory
would exhibit population declines. The net
effect of such fires on spotted owls is unclear. A
fire that removes the tree canopy would likely
render the area unusable for foraging because of
how spotted owls forage. But if the spatial extent
of crown loss is limited, a mosaic is created that
could provide a diversity of prey for the owl and
actually be beneficial.
Clearly, research is required to determine the
effects of fire on spotted owl prey. Because owl
prey species evolved in ecosystems where fire was
a natural process, we assume that these species
survive and some even benefit from the occurrence
of fire. Fire has been excluded from most
southwestern ecosystems during the 20th century,
resulting in systems where fire behavior
may deviate substantially from natural conditions.
Effects of fire on small mammals under
present environmental conditions are unclear.
Volume II/Chapter 5
40
Timber Timber Harvest Harvest and
and
Fuelwood Fuelwood Removal Removal
Removal
Mexican Spotted Owl Recovery Plan
Numerous silvicultural methods are used to
harvest timber in the Southwest. These include
both even-aged (predominantly shelterwood
systems) and uneven-aged (e.g., single tree,
group selection systems) management. Further,
these systems are applied differently according to
site characteristics and management objectives.
Given the various scenarios for silviculture,
generalizing about their effects on prey populations
is not possible.
Tree removal, whether to harvest sawlogs or
fuelwood, will affect natural ecosystem processes
in numerous obvious and obscure ways. Certainly,
removal of mast-producing trees (e.g.,
pinyon pine, juniper, oak) reduces food availability
for several of the owl’s prey species. Also,
removal of tree biomass from the site will interrupt
both nutrient cycling and energy flow. The
effects of altering these processes on owl prey
populations is unknown, but the disturbance
may likely benefit some species while negatively
affecting others. Tree removal and accompanying
site disturbance during and following removal,
plus residual disturbance such as soil compaction,
increased erosion, and creation of slash
piles, will directly alter habitats of many prey
species. Block and Ganey (unpublished data)
found more deer mice in areas with slash than
areas without slash. In the same general area,
Goodwin and Hungerford (1979) noted that
brush mice and Mexican woodrats used long
windrows of slash following logging. Block and
Ganey (unpublished data) sampled the same
areas 18-20 years after the Goodwin and
Hungerford study and captured few woodrats
and brush mice. This suggests a temporary
benefit of slash piles in that they may provide a
short-term habitat component that is not used as
the slash becomes compressed and decomposes.
As noted above, effects of tree removal on
small mammals varies by prescription and site
characteristics. The effects are somewhat scale
dependent. Prescriptions for even-aged,
shelterwood cuts or clearcuts effectively return
large areas, the size of stands or greater, to earlier
seral stages. Small mammal community structure

is correlated to plant seral stage (Fox 1990,
Kirkland 1990). Thus, following even-aged
management, populations of some species will
respond positively and others negatively. As time
progresses and vegetation proceeds through
succession, population dynamics of species will
change in response to changing habitat conditions
and community structure. Areas subjected
to even-aged management may not provide
appropriate foraging habitat for the spotted owl
(see Ganey and Dick 1995). This means changes
to small mammal populations within the harvested
areas may not affect the owl prey base
directly because those animals may not be
available to the owl. However, the same small
mammal populations may provide a source of
individuals that disperse into adjacent owl
foraging habitat.
Uneven-aged management would likely be
used over large areas and does not create small
stands, but rather it creates groups or clumps.
Mosaics of habitat provide diverse plant communities
and other conditions that, collectively, can
support a rich diversity of fauna. Populations of
different species may respond variably to aspects
of the mosaic pattern, such as conditions within
each patch type, patch size and shape, and
interspersion and juxtaposition of these patches.
Mosaic patterns resulting from timber management
prescriptions such as single-tree or group
selection cuts may in some ways mimic natural
disturbance patterns and create canopy gaps.
This does not imply that effects of silviculture
are equivalent to those of natural disturbance,
only that the resultant spatial patterns are somewhat
similar.
Clearly, research is needed to determine
cause-effect relationships of tree removal on
spotted owl prey populations, the hunting ability
of the owl, and the mosaic patterns which best
conserve owl populations. Such research will
entail experiments conducted at varying spatial
and temporal scales to understand the true
magnitude of the effects. Until these experiments
are conducted, effects of tree removal on
prey habitat and populations must be based on
speculation and conjecture. Future management
conducted within a scientific and experimental
context may provide a means for establishing
Volume II/Chapter 5
41
Mexican Spotted Owl Recovery Plan
cause-effect relationships (see USDI 1995:
Activity-Specific Research Section, Part III.E.).
Grazing
Grazing
The effects of livestock and wildlife grazing
on spotted owl prey populations and their
habitats is also a complex issue. Impacts can vary
according to grazing species; degree of use,
including numbers of grazers, grazing intensity,
grazing frequency, and timing of grazing; habitat
type and structure; and plant or prey species
composition. It is well documented and intuitive
that repetitive, excessive grazing of plant communities
by livestock can significantly alter plant
species density, composition, vigor, regeneration,
above or below ground phytomass, soil properties,
nutrient flow, water quality, and ultimately
lead to desertification when uncontrolled
(Kauffman and Krueger 1984, Orodho et al.
1990, Vallentine 1990, Milchunas and
Lauenroth 1993). These effects can have both
direct and indirect adverse impacts on animal
species that are dependent on plants for food
and cover. However, moderate to light grazing
can benefit some plant and animal species under
certain conditions and in certain environments,
maintain communities in certain seral stages,
and increase primary productivity (Reynolds
1980, Hanley and Page 1982, Kauffman and
Krueger 1984, McNaughton 1993). Further,
direct influences of livestock on plant communities
are not always reflected in small mammal
communities (Grant et al. 1982). Thus, any
generalizations presented here should not be
construed as absolute; there are exceptions.
No studies document the direct and indirect
effects of livestock and wildlife grazing on the
Mexican spotted owl or its prey (see reviews by
USDA Forest Service 1994, Utah Mexican
Spotted Owl Technical Team 1994). We found
only one study that specifically investigated the
effects of livestock grazing on an upland forest
owl, the tawny owl (Putnam 1986). However,
the design and limited sampling effort of this
study prevents extrapolation to the Mexican
spotted owl. Interpretive extrapolations are
further hampered because most livestock-effects
studies on small mammals have been conducted

in shrub-steppe, grassland, or riparian communities
of arid or semi-arid regions (Kauffman and
Krueger 1984, Milchunas and Lauenroth 1993).
Except for the possible use of these areas for
dispersing or wintering, such areas are not
typically used by Mexican spotted owls.
Despite the dearth of specific information
about spotted owls and grazing, there exists some
knowledge regarding the effects of livestock
grazing on small mammals frequently consumed
by spotted owls and regarding mesic or montane
plant communities inhabited by the owl’s prey.
Relevant studies include Hanley and Page
(1982), Medin and Clary (1990), Schultz and
Leininger (1991), and Szaro (1991), and are
briefly summarized below.
In a 250,000-ha (619,250-ac) area of the
Great Basin, Hanley and Page (1982) found that
livestock grazing (primarily cattle with an
average of 0.16 animal unit month, April to
October during each of four consecutive years)
generally increased shrub composition and
decreased perennial herbs and grasses (primarily
tall bunchgrasses). However, these effects depended
upon community type. Shrubs increased
in grazed wet meadows and willow-riparian
communities, whereas tree-form willows decreased
by 60%. Herbaceous layers were 30-50
cm (11.8-19.7 in) deep in ungrazed meadows
compared to the “mowed” appearance of grazed
meadows. Reduction of graminoids and forbs
increased structural diversity in mesic habits by
increasing shrubs but decreased structural
diversity in shrub-dominated, xeric habitats. The
authors postulated that the loss of perennial
grasses and herbs caused lower numbers of desert
woodrats, and long-tailed and mountain voles in
grazed meadows by decreasing food sources and
cover. The authors also reported a greater number
of Great Basin pocket mice, deer mice, and
least chipmunks in mesic habitats grazed by
livestock compared to ungrazed, mesic habitats.
However, these same three species decreased in
xeric habitats grazed by livestock.
Schultz and Leininger (1991) examined the
effects of cattle exclusion along one 5-km (3.1mi)
length of a riparian community in
northcentral Colorado. During the summers of
1985 and 1986, plant and small mammal
communities were sampled for comparison
Volume II/Chapter 5
42
Mexican Spotted Owl Recovery Plan
between adjacent grazed areas and three
exclosures established in 1956 and 1959. Plant
communities varied from grass-herb-sedge
lowlands to ponderosa pine uplands. Observed
differences included greater vascular vegetation
cover, graminoid cover, and shrub cover in the
exclosures. Litter accumulation in the exclosures
was nearly twice that of grazed areas, and willow
canopy cover was 8.5 times greater (Schultz
1990). Deer mice were significantly more
abundant in grazed areas and western jumping
mice were significantly more abundant in
ungrazed exclosures. Seven species of small
mammals were found in grazed and exclosed
areas, although species composition in each area
was slightly different. Deer mice, least chipmunks,
masked shrews, dusky shrews, and
western jumping mice were found in both areas.
Long-tailed and mountain voles were not observed
in grazed areas. Northern pocket gophers
and golden-mantled ground squirrels were not
found in exclosures.
Medin and Clary (1990) compared small
mammal populations between a riparian habitat
seasonally grazed by cattle to an adjacent 122-ha
(302.2-ac) riparian exclosure which had been
protected from livestock grazing for the previous
14 years. They found that mountain voles were
four times more abundant within the ungrazed
exclosure as compared to the grazed riparian
habitat. In addition, vagrant shrews, water
shrews, and northern pocket gophers were only
trapped within the ungrazed habitat. Consequently,
they noted that small mammal species
richness and species diversity were higher within
the ungrazed exclosure despite the fact that total
population density of small mammals was a
third higher in the grazed portion due to the
high numbers of deer mice.
Szaro (1991) examined the effects of grazing
along the Rio de las Vacas, a montane stream at
8,528 ft (2,600 m) elevation in the San Pedro
Parks Wilderness Area, New Mexico. Terrestrial
fauna within two 900 x 50 m (2,952 x 164 ft)
livestock exclosures were sampled and compared
to downstream private lands that were continuously
grazed. Small mammals were sampled each
month, June through September, in 1985 and
1986. He found greater amounts of herbaceous
vegetation in the exclosures. Greater numbers of

small mammal captures were observed in both
exclosures in 1985 compared to grazed areas
downstream. Small mammal captures were
reduced and indistinguishable in 1986 but some
cattle trespass had occurred into the control
exclosures. Fewer species were captured in the
grazed areas. Mountain voles and deer mice were
found in both grazed and ungrazed situations,
whereas least chipmunks and golden-mantled
ground squirrels were found only in ungrazed
areas.
Other studies have shown similar results:
lack of a numerical decrease by deer mice to
grazing (Reynolds 1980), and significant decrease
in voles caused by grazing induced loss of
cover in mesic habitats (Grant et al. 1982). If
these general patterns can be applied to upland
habitats of the Southwest, we would expect
moderate to heavy grazing to decrease populations
of voles and improve conditions for deer
mice in meadow habitats. Such decreases could
negatively influence spotted owls occupying
areas in the Upper Gila Mountains, Basin and
Range - East, and portions of other RUs where
voles are common prey or used as alternative
food sources when other prey species are diminished.
Increases in deer mouse abundance in
meadows probably would not offset decreases in
vole numbers because voles provide greater
biomass per individual and per unit of area. Loss
of perennial grass cover in xeric communities
used by owls, specifically, ponderosa pine forest
and pinyon-juniper woodlands, due to grazing
may reduce deer mice and Mexican vole populations.
The reduction of these prey species in
xeric communities could be more critical than
that in meadows if xeric habitats are necessary
for winter foraging by the owls.
Finally, high intensity grazing in riparian
communities during the fall and winter seasons
where grass seedheads may be totally removed
can cause significant short-term decreases in
small mammal populations (Kauffman et al.
1983). Continued heavy grazing in upland or
lowland riparian communities could therefore
greatly reduce the potential for utilization by
foraging, dispersing or wintering spotted owls.
Volume II/Chapter 5
43
Mexican Spotted Owl Recovery Plan
CONCLUSIONS
CONCLUSIONS
Mexican spotted owls consume a variety of
prey throughout their range but commonly eat
small and medium-sized rodents. However, the
owl’s food habits vary according to geographic
location. For example, spotted owls dwelling in
canyons of the Colorado Plateau take more
woodrats, and fewer voles and birds than do
spotted owls from other areas. In contrast,
spotted owls occupying mountain ranges with
forest-meadow interfaces, such as the Basin and
Range - East, Southern Rocky Mountains -
Colorado, and Upper Gila Mountains RUs, take
more microtine voles The differences in diet
likely reflect geographic variation in population
densities and habitats of both the prey and the
owl.
No strong rangewide relationships appeared
in our analyses of the owl’s diet and reproduction.
The relationship was positive and nearly
significant when comparing the prevalence of
the three most common prey (peromyscid mice,
woodrats, and voles) in the diet and owl reproduction,
implying that multiple species influence
the owl's fitness. However, this generalization
may not apply to owls in the Sacramento Mountains
where the owl's reproduction appears most
influenced by deer mouse abundance. In addition,
the predominance of woodrats, both in diet
frequency and biomass throughout much of the
owl’s range, suggests that a single prey may
influence the owl’s fitness. Other studies have
shown positive associations between larger prey
(e.g. woodrats) in the diet of northern and
California spotted owls and its reproductive
success (Barrows 1987, Thrailkill and Bias
1989). The lack of more specific results should
not imply that a simple relationship between
diet and reproduction or other fitness measures
does not exist. Rather, those relationships are
more complex than are evident by the available
information and analytical approaches used in
producing this report. In most cases, total prey
biomass is likely more influential on the owl’s
fitness than the abundance of any particular prey
species. Other factors worth exploring would be
lag effects such as the effects of winter diet on
breeding potential, prey diversity, or synergistic

effects of diet with factors like owl density,
weather, and habitat.
Studies conducted in four vegetation communities
demonstrate that abundance of the
owl’s food varies according to habitat and time.
In the Sacramento Mountains, the greatest prey
biomass is found in high-elevation meadows
occurring along riparian corridors. Common
prey species occupying these meadows are longtailed
voles, Mexican voles, and deer mice.
However, abundance alone does not necessarily
connote availability. Availability infers cooccurrence
of owl and prey plus coincidental
vulnerability to predation and ability to capture.
Successful capture of meadow-dwelling rodents
may be restricted to areas near forest edges
coinciding with the presence of foraging perches.
Rather, meadow habitats may play an indirect
role by producing high densities of prey that
become available to owls following dispersal into
adjacent forests. Owls in the Sacramento Mountains
consume a moderate-to-large proportion of
voles during years of high vole density.
Summer prey biomass in mesic (mixedconifer)
forests can be greater than in xeric
(ponderosa pine-pinyon-juniper-oak) forests of
the Sacramento Mountains for two reasons.
First, all five prey species common to this owl
occur in mesic forest, whereas only four occur in
xeric forests, where long-tailed voles are absent.
This vole can provide an average mass of 32 g
(1.1 oz) to an owl and it is the second most
abundant species occurring in the mesic forests.
Second, deer mice dwelling in mesic forest can
attain great summer densities during certain
years. This same pattern has not been observed
in the seemingly more stable xeric forests. Prey
composition and abundance in ponderosa pine-
Gambel oak forests of northern Arizona are
similar to the xeric forests of the Sacramento
Mountains. In both areas, deer mice are ubiquitous
and the Mexican woodrat and brush mouse
are patchy in distribution and abundance. In
contrast, Mexican voles are apparently less
abundant in pine-oak forests of northern Arizona
compared to xeric forests in the Sacramento
Mountains. Whether low densities of voles in
this forest type are natural or the result of past
management activities is unknown. However,
decreases in herbaceous biomass resulting from
Volume II/Chapter 5
44
Mexican Spotted Owl Recovery Plan
unnaturally dense forest conditions may explain
low numbers of voles in these forests.
Arranging the four vegetation communities
according to summer prey biomass indicates that
meadows > mixed-conifer forest > ponderosa
pine-pinyon-juniper-oak woodlands > ponderosa
pine-Gambel oak forest. When considering
other factors that influence the availability of
prey, mixed-conifer forests likely provide the
greatest amount of food during summer periods.
Rearranging the same communities according to
winter prey biomass indicates that meadows >
ponderosa pine-pinyon-juniper-oak woodlands >
ponderosa pine-Gambel oak forest > mixedconifer
forest. Accounting for the availability of
prey, woodlands with a mixture of ponderosa
pine, pinyon-juniper, and oaks provide more
prey to owls during winter months than the
other three communities.
Prey biomass is usually greater in all communities
during summer periods when owls raise
their young. However, temporal peaks of prey
cycles are not correlated among vegetation
communities. That is, when prey are abundant
in mixed-conifer forest one year and low a
subsequent year, an opposite pattern may occur
in a different vegetation community. The
asynchrony of abundance among prey species,
vegetation communities, and time may provide a
buffer against the effects of extreme oscillation in
prey cycles. This implies the importance of
maintaining a mixture of vegetation communities
to ensure a diverse and abundant prey base
within the owls foraging range.
An important concept exemplified by our
analyses is that the habitat of each prey species is
unique. This finding clearly indicates a need for
providing a variety of conditions which are used
by the different species of prey. For example, in
the ponderosa pine-Gambel oak forests of
northern Arizona, deer mouse abundance shows
little variation according to forest structure and
composition whereas Mexican woodrat and
brush mouse abundance are strongly correlated
to understory characteristics, specifically log
volume and shrub cover. Further, Gambel oak
density is greater within habitats of the woodrat
and brush mouse than occurs randomly in the
forest. These habitat components are rarely
considered in planning forest management

activities but should be to provide appropriate
habitat conditions for these prey species. Obviously,
conserving habitat for a diversity of prey
may help buffer against population fluctuations
of individual prey species and provide a less
stochastic food resource for the owl.
The consequences of three common disturbances
(fire, timber/fuelwood harvest, and
grazing) on the owl’s prey and habitat depends
on many factors. Often ecological tradeoffs
result, making exact predictions difficult. Some
prey species may increase, while others decrease
for a given disturbance. More detailed predictions
about the influences of these disturbances
must await more specific research. In general,
management practices that lead to discernible
reductions in total prey biomass or diversity over
large areas will not promote owl recovery.
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Volume II/Chapter 5
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Mexican Spotted Owl Recovery Plan
APPENDIX APPENDIX 5 55a
5
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